IE

Hi ,
I am just curios why the beautifull them roller ( and the good css
framework ) are so heavily based on css3 ( ex: corners ).
Is not sure that IE will implement this in IE8 ...... so we will be
forced to have jquery UI bad rendering in IE for maybe the next 2
years......
At th eend IE is 70% of market ....so why this choice???
What do you think??
Andrea