So the Premium Edition has been announced for PC, Xbox 360, and PS3. But many many many people are disappointed that the DLC is not included. A GOTY Edition is long overdue.
Though, could this mean that Bethesda is confident that DLC will finally arrive for PS3?

They could have easily just announced GOTY Editions for PC and Xbox 360 and not PS3 since the majority of their players are there but they haven't.

it's because they are not finished with dlc

No. Because this isn't the same as a GOTY year edition. It's a cash grab for the holidays that repackages preexisting content rather than create new content. It also allows them to make more money through DLC, considering Hearthfire hasn't even been out 2 months. They'd be fools to give it away already.

Summer or Christmas 2013 is when you can expect a GOTY edition, most likely. That's when all the DLC should be out.

I've heard that suggested, i.e.: 'premium edition means there will likely be DLC for PS3', but I'm dubious. I rather suspect that the reason they're releasing this, rather than the expected 'dlc included' GOTY is that given a: revenue from a GOTY edition is expected of them this quarter, but b: they can't release a platform-restricted version without worsening what is already a PR disaster for them PS3-wise, they are, therefore releasing this "Premium" (not GOTY) thing with the T-shirt, trading cards, flavoured condems, and whatever else they can toss in the box.

To make a comparaison, when did you ever think your favourite band coming out with a coloured-vinyl re-release ever presaged a new single coming out.

Wait are these condems made by the same guys who ported the PS3 version? Prepare for babies...