Vaderisnothayden said:

It most definitely does detract. It increases the ridiculous end of ROTS = start of ANH factor, making the universe yet smaller.

I don't think I understand what you mean by this.

So nothing changes in 20 years. Tarkin goes with the Death Star...

I think that's an interpretation you have to choose to make. It's not like it's laid out in front of you waving a Mr. Obvious cap. You can't say that, just because Tarkin took a brief stroll across a Star Destroyer's bridge whilst overseeing the Death Star's construction one afternoon, that he hung around for an extra 20 years after that.

...which should never have been in the prequels.

Yeah, I'm forced to agree.

Nor is Tarkin's appearance merely an easter egg like those things you mentioned..

You're right, I could have described it better. Easter Egg is not the right term. It is similar to an Easter Egg in that, yes, it is fan service. However, it's harmless fan services as opposed to obtrusive fan service (EX: Boba Fett in AotC, Chewbacca in RotS, or the Death Star in the PT).