Verily, you can't just look at the date the announcement was made in isolation. You have to look at when it was made relative to when the convention was held. IIRC, in every one of those cases except for Kerry/Edwards, the announcemet was made just days before the convention. The announcements this time around are likely to be late in calendar terms because the conventions are so late.
True, I hadn't been thinking about that. But I also think that, with tradition being broken, candidates are much more likely to announce at a politically convenient time (as early as c. July 10 being possible) rather than the traditional time.
Well, you've also got to account for the fact that the selection and vetting process is extremely thorough these days. It takes a really long time, and the Obama campaign got a late start at it (because the Democratic primary contest went longer than it had gone in years this time). So that points towards Obama making his choice rather late. McCain started much earlier, but, as Erc said, McCain has a strategic advantage with a later convention, in that he can wait to see who Obama picks first, and then take that into account when making his own decision.
