*laughs* Marketing... While megapixels isn't everything, the XTi does have some features that are impressive for it's price.
What happened (IMO atleast) is that Canon decided (sales dictated that) they need to get their entry level DSLR in the 10 megapixel range to keep up w/ the Nikon. Even though megapixels aren't everything, they are a big selling point - especially for the entry-level DSLR market.
In doing so they introduced a few new features that we will probably see trickle in some form into the next lineup. For example the self cleaning sensor is much needed - and although it isn't as good as the Olympus system it is still VERY welcome.
I don't think any more bodies will be announced this year, but I would venture to guess (and hope) that the 30D (cough - 20D MKII) will receive a face-lift as well as their oldest body the 1D MKII with some of these new features sometime soon here.
Why they re-did the 30D with such little substance is unclear - but it was obviously marketing driven, and I bet it worked!