Actually, if there are online achievements you're paying to unlock those as well, so there's little room for complaint because one way or another they're going to attempt to get more of your money. As for DLC, bad news and worse news; the bad news is if they can find a way to exploit customers for more money they will, the worst news is that all too many people are perfectly okay with being exploited. Millions in sales for a map "pack" that offered only 4 maps for $20 proves that people are okay with being hosed, so game companies have little reason to stop hosing their customers.
Like you, I have an appreciation for getting 100% in a game, my gamertag speaks for me on this, but the best thing I ever did for myself was turn the notifications off. Those things serve no purpose other than to bait you into paying more for a game than you should. I've yet to play a game where these things were clever, or funny, or anything that wasn't filler or meant grinding, or shelling out extra cash. It was a good concept, but it's so badly executed that most people either don't care at all, or they care too much. Pretty soon you might find yourself basing your purchasing choices on the type of achievements that are in the game and whether or not it'll cost you an arm and a leg just to get them all. It's not your fault, it was designed to influence how you think about the game you purchase and play.
Not worth it.