Actually it'd be a guaranteed win in the EU, since our courts routinely side with consumers over corporate interests. Oddly enough, I haven't heard of this bug here, but you can rest assured it wouldn't even need to go to court, as it's eight kinds of illegal already.
And no, this case is not retarded. Since Apple wants to use phone numbers (a regulated identifier) for their proprietary IM instead of Apple IDs, they have to make sure their implementation doesn't break the functionality of text messaging.
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EULAs are about as legally binding as soiled toilet paper, and this bug isn't on the phones of the people suing Apple, and therefore the EULA doesn't even apply to them. Rather, they are suing Apple because the iMessage system itself is defective and is breaking the functionality of SMS.
If US carriers had any backbone, they'd sue Apple themselves.