What impact does the writing system has on the concept of what constitutes a language?

I read the following content from one of my Prof's book with keen interest.

" Much to the chagrin of modern linguistics, which treats only the spoken as real language and writing as a secondary indication of speech, the fact is that cultures generally recognise themselves as having 'the same language' so long as they share the same written language, regardless of how much variation there may be in how they speak." - John E.Joseph, Language and Politics, 2006,Pg 28

Joseph states the example of the Arabic speaking world, where Muslims and Christians Arabic mother tongue speakers view the classical written language as the original and correct Arabic, the difference only being Muslims view the written Arabic language with an addition perspective, that of the sacred authority of Koran. Then he continues exemplifying his notion with the example of "the family of Chinese languages".

" More dramatic however is the effect of a non-alphabetic writing system, and particularly the Chinese system of character writing. Chinese characters are logographs, which is to say that each character represents a word. Some characters are basic and cannot be broken down... ... However, despite the inclusion of phonetic elements, the characters do not analyse each word into its component sounds the way alphabetic writing does. The result is that a character such as 然 corresponds to the spoken Mandarin word ran, the Cantonese jin, and the Wu zφ, each pronounced with a different tone in addition to the consonant and vowel differences. Yet speakers of Mandarin, Cantonese and Wu, while fully aware of the divergences and of the fact that they cannot understand one another's speech, are entirely certain that there is one single Chinese word 然 that they are each saying in their particular dialectal way. When asked why they believe this, the proof they cite is usually the existence of the written character, which is the word as far as they are concerned. " (Joseph, 2006)

He contrasts this example with the English 'yes' and German 'ja' and concluded that

"whether different writing systems caused the different ways of thinking about words,or vice versa, is a chicken-and-egg question... ...the Chinese system, by allowing so much more latitude in the visual-sound link, enables belief in a single Chinese language much more robustly than an alphabet does, even for a pair of languages as closely related as English and German. Yet neither determines the cultural beliefs in question......"

He was actually talking about the relationship between language, politics and national identities. He concluded the paragraph citing the case of Taiwan maintaining the traditional writing form as a choice with "political motivations and ramifications", using it as a potent way of performing a distinct national identity.

This isn't any new conclusion for me. What interest me is the contrasts shown in my perception of Chinese as a language and the way modern linguists define a language. This was a point of contention at the beginning of term, as a seminar room of Chinese speaking students had to clarify what constitutes a language in the study of linguistics. By virtue of the way I learn the language in school, and by virtue of various experiences where I was able to clarify my reception of speech with dialect speaking elders or differentiate allophones in the language through the written forms, I had, as exemplified in the text above, view the basis of my language as the written form of the words themselves.

In fact, I had tried to explain to my Kazakh friend that the Chinese language is a totally differnt world and since unification of the written form took place way in B.C times, the modern linguists classification of what constitutes a distinct language may not work well for analysing the Chinese language. The question about "What's the Chinese language like?" was posed by my Kazakh friend as she explained that with the establishment of the new nation, their people work hard to establish the standardised Kazakh language. I didn't really understood what it really meant then, since I reckoned that the Kazakh language has been around for a long time. I had thought that it only meant efforts to revitalise and enhance the vitality of the language, as the Russian language had been widely used during the Soviet years. That was in Week 1 of school. Finally, as term progresses, I realised that things aren't that simple. What intrigues me even more is the choice of representation for this language, as it has been represented by the Latin, Arabic and presently the Cyrillic form. Pardon my poor knowledge in the Philology of world languages but this was definitely unraveling for me. 

In retrospect, the most intriguing question in my mind now is, then how important is the writing system in the Chinese language? To me, the writing system for the Chinese language probably has a higher weightage than its counterparts in other languages. This is all too familiar as I recall students who can speak Chinese but can't really write asking the teacher innocently " 为什么'中间'的‘中’means 'middle',可是zhongdian 的'zhong; means 'the end'?  As some foreign modern linguistics continue to fret over the fact that Chinese is not going to be abandon its "complicated" writing system and romanise the language anytime soon, enthused Chinese foreign language learners would probably get an introduction to the Chinese written language that looks like this. Now my question is, by teaching students only the spoken form and the typed-input form of the language, how will this change the way we cognize the language?    

And to end this off, I found an interesting link about the Vietnamese language.