Kragil already makes a good point, but there were more reasons why a delay
of 4.0 would've been bad.
For example. NVidia would've continued to ignore our complaints about the
lack of proper XRENDER acceleration. The "better 4.0 release" would
therefor still have had horrible performance and corrupted systemtray
icons. Even 4.2 suffers, on some installs, from those issues - X.org and
the driver developers haven't been able to fix that in the last year. The
same goes for more pieces of technology, major functionality in Qt being
one of them.
Another reason to release was to get more developers. Because as you might
know, a FOSS project depends on developers, and doesn't really care about
users. Users only eat time away from the actually useful stuff:
development. The 4.0 release succeeded in this regard: over 300 new
developers in the last 12 months.
There are more reasons for releasing 4.0 when we did, but I hope I managed
to make clear that there was more than "the end users will love this". End
users were simply not the target for this release, we did it for other,
equally (if not more) important reasons.
The only thing we imho could've done better is the release announcement
itself (compare it with the 4.1 announcement and see that we DO learn).
Pretty much every other piece of communication was handled well.