Because copying out text is extremely aggravating, the author is encouraged by the poverty of the medium to reduce the amount of text copied. This results in shorter, clearer, more concise text. Moreover, whilst copying, the author is forced to examine the whole work much slower than if she were just reading it again. Thus, she won't be able to just "gloss over" text that would otherwise require a closer examination.
For software developers, an analogous case would be Wiki:CrcCards that force design simplicity by being both too small to write bloatware on and by forcing this labour-intensive copying procedure every so often. So also WhatIsReworking.
My father (who worked in software from the 60's to the 90's), used these same arguments to advocate punched cards and batch compilation instead of online editing/compilation. He felt that the poverty of the medium (the long turnaround time, the laboriousness of making changes) sharpened the programmer's thought and maximized the chance of "getting it right first time".
Somehow, I think the richness of a medium brings greater benefits than does its poverty. And we don't see many punched cards nowadays.
Between the time online editing was being invented and the time it became accepted there was much development in terms of editing ergonomics. At a certain point, the poverty of the old medium is overcome by the efficacy of the new. Note that Rational Rose and Together really suck. Hence, CRC cards are better.
There's a sub-issue lurking here: does the default keep content or lose it? The question arises even in non-impoverished media. For example, a copying garbage collector/memory manager will keep only wanted content and then delete everything which remains.
On current Wikis, all content is kept by default. It might be interesting if content expired by default instead, and some explicit action had to be taken to preserve it (ie, CommunityWiki:StablePage). I think this makes most sense for ThreadMode contributions. We might evisage a page divided in two, with a DocumentMode consensus above the line and ThreadMode conversations below the line.
SlashDot seems to do that with their rating system; unhelpful comments tend to "drop off the radar screen."