They've already been bitten by that one. They
blocked all browsers except IE [news.com] from accessing MSN.com. After two days of people making noise about it they let everyone view MSN again.
Did they learn? No.
Less than two years later [cnet.com] they served a stylesheet to Opera (and only to Opera, other browsers received a working stylesheet and IE had its own) that deliberately broke the display of the page. They served Opera the IE stylesheet, which displayed fine, after some more complaints.
Was that enough for them? No, they tried again with hotmail.
They sent Opera an incomplete javascript file [opera.com] that was missing a required function to empty the junk e-mail. Other browsers were sent a different javascript file.
I don't think they'd dare try again with how closely the EU is monitoring them now.