The difference is, with other releases there hasn't been a time pressure. The last albums came when u2 as a band wasn't doing anything - they'd release the album, then plan a tour around it.
Whereas this time, given the (relatively) poor reception of the NLOTH songs live, as well as returning to tour in the US 2 years after that album was released, i believe they want something new to spice up the tour, and avoid a 'greatest hits' thing.
If they release something in november, they'll have wasted the opportunity to tour with it. It will be a tour-less album, and i just don't see u2 releasing something immediately after a massive tour.
May is the opportune time to release it, because they'll be about to play many dates in a region they already visited in a previous year, and will need a reason for the setlist to be different.
And Zooropa man , it's not like we've heard nothing - we've heard the producer they're using, we've heard that by october they had 12 songs with him, we've had the freakin' manager say the album was being polished off ready for a may release.
The lack of buzz could very well just be a reaction to the over-blown promotion to NLOTH, which didn't really help the album. Even if not, there's plenty of time for the album to be promoted, if we have 4 months to go.
I'd say don't worry about it... at least not for another few weeks