launch like that would be impossible today , we would know about it through leaks etc..
Apple does the "launching today/sometime in the next 2 weeks!" thing all the time. It wouldn't be impossible.
The problem with the Saturn wasn't really the "in stores today!" part. It was 1) it didn't have all that much build up especially with all the preceding Genesis peripherals, 2) it was only "in SOME SELECT stores today!" which utterly pissed off a host of major retailers and poisoned the Saturn's position in the market, and 3) developers had no idea it was happening, so games weren't even close to ready.
That last point there is the main reason why Sony isn't doing a "launching today!" thing at Gamescom. Its biggest launch titles are all holiday releases that wouldn't be launching for a couple of months.
Even an October launch is a little early for some of its intended launch titles. Watch Dogs, for example, isn't hitting any other platform until November 19.