A software engineer responds ...
All software is full of bugs.
Over the years computer software has become more and more sophisticated often involving millions of lines of code. It is a practical impossibility to test every path through the software and eradicate every bug.
Here is a little test for you - try writing a one or two page document (any subject, doesn't matter), read it, correct any errors you spot in spelling or grammer. Now give it to someone else. How many mistakes do they spot. Multiply that by the "millions of lines" factor above and weep.
Add on the fact that every piece of software we now write is dependent on many many millions of lines of other peoples software underneath it - the operating system, graphics card drivers, sound card drivers, ... weep some more.
Then there are numerous flavours of the operating system to contend with Windows 98, NT, 2000, XP (at least three flavours of that alone) ... weep some more.
You have to draw a line when you think it is good enough to let out the door - and, yes, economics does come into it.
Then there is the fact that one persons bug is another persons concious design decision. It is dismaying, but not surprising any more, how often I see "this bug must be fixed" comments that are talking about something they don't personally like about the design of the game - not a bug at all.
I personally love this idea of going back to the old version, it could be quite a refreshing and eye-opening experience to see just how much has changed in a few short months.
Incidentally - the person asking why its called a bug - see this Wiki article:
Wiki - software bug