It is progress, but I agree, why select the date that is already selected, unless you want to change it?
I can see the rationale behind it, viz. move to the next field after having selected certain information (e.g. after selecting an origin, move to destination, then dates), however it's a flawed logic to do so automatically without consideration of context, i.e. as you have pointed out.
I have no idea whether this kind of automatic change of focus is better for those using tablets, but for those using a mouse on a PC it is quite annoying. Especially as loading the calendar seems to use a few too many tics to pop up compared to normal.
On that note, that's another thing that annoys me, too - the calendar. To select a date on the calendar that is many months in advance, you need to keep clicking (or tapping) the ">" symbol on the right of the calendar. The problem is that you can't just click quickly on the button to skip ahead quite a few months - you need to click then wait for the panel to update before trying again. This is rather painful if you're looking for flights even about six months ahead. Worse, if you keep clicking and for some reason you click on a blank space rather than the ">" (either inside the calendar panel or just outside it), sometimes the calendar panel disappears, then you have to click on the calendar icon again to bring up the panel, and start all over again!
Something like either a drop down menu on the month or the 12 months as buttons at the top of the calendar panel (the latter is a la the old Qantas site) would make selecting dates a lot quicker. Also, it shouldn't matter if you have a beast blasting 3 GHz with 8 GB RAM or a Celeron 1 GHz with 2 GB RAM (or even less than that) - it should not take longer than 0.5 seconds (or even 1) to load up a calendar panel.