I would absolutely love it if this happened. In the Zombie commercial @ 0:10, the guy pulls out his 925 and while he's glancing at the time, the Windows logo is also blinking. So even though people are reporting that it's just for when the battery is critically low.... we have this little oddity in the commercial to digest.
The only other reason I can think of for Nokia doing this (other than teasing an upcoming notification feature) is that Nokia simply chose this way to advertise that it's a Windows phone. I just feel like they could have done that in a different way, for example, showing the live tiles). And they wouldn't advertise a "notification light just for critical low battery" because that's just weird, no one advertises something basic like that - you don't want one of your selling points to be "hey, when your battery inevitably dies completely, we have this logo thing that blinks!" and clearly he still has plenty of battery in this commercial. I may be delusional, but I think we can look forward to a proper notification light in the future. If not, we all need to complain that the commercial is misleading and maybe it'll happen, haha. I can dream...