Speculation...

Because eventually there's nothing left to improve and/or no 
(financially acceptable?) way to implement desired changes / advances in 
technology / whatever until you let go of old technology that's keeping 
you from advancing further.  (And because you don't want to completely 
rewrite that old technology and/or write a way to embed that old 
technology into your new technology - especially when there are ways for 
the end user to accomplish that already (keep the old box, VM Ware, etc.).

I think to date, MS's OSs (hee hee, I made a rhyme) have basically been 
modifications of the previous version (regardless of whatever hype 
they're selling).  Maybe now they're trying to get away from that model...

Someone posted a link here to an article about an internal battle in MS 
between the "keep backward compatibility" camp and the "bag that and 
move forward faster" camp and which was winning.  It was old, as I 
recall, but interesting.  No idea on the accuracy of the article or 
where exactly Vista lies between the two...  (I seem to recall reading 
somewhere that since its inception, Vista has take great strides 
backward and isn't that big a change anymore, but then I don't pay a lot 
of attention to these things.)

FWIW,

Liz


Anders Jonsson wrote:
> Why would Microsoft drop all 
> support for 16-bit programs or/and DOS programs in Vista? What would they 
> gain by removing that possibility? Wouldn't that just affect the sales 
> figures? If you can't runt your old programs you might not upgrade.