I'll point out that the in-game "offer", as it were, doesn't use out-of-game language. You are offered a quest, or a journal entry, the same way that you would get any other quest. No turning to the camera and offering you a delicious Coke or anything of the like. If you accept, you are briefly taken to the DLC page to grab the content -- if you have not already done so. If you have, you won't even notice the difference. It will also be a simple enough matter to refuse the quest -- you don't have to endure a commercial.
Picturing scenarios where there are in-game neon billboards and NPC Shamwow salesmen trying to lure you conveniently into spending more money, and then railing against it, is a bit over the top. (It's the internet, though, right? Who'd have thought?)
Although I do like the idea of the Shamwow guy as a pushy dwarven merchant, now. Hmm. I'll have to make a note of that.
It's a way to insert the DLC into the overall game, nothing more. If you don't like the idea even of that interface (I suppose some people are going to object to the notion of DLC daring to sully their gaming experience no matter what), then that's up to you -- but at least get it straight what you are objecting to.