Dealer techs are underpaid (per hour) and get flat rate - if they want to make any money, they have to bill 50+ hours per week and get it done in under 40. So when you bring your car in, they're going to try to sell you their high-profit stuff. The tech probably gets paid half an hour to do a fluid change that he can do in 10 minutes or less. Buddy of mine works at a Volvo dealership and he says he'd do oil changes all day long if he could, just for that reason.
That's also why they often have so much trouble reproducing an issue. They don't get paid the hours to take the time to find the problem. If it takes them more than the hour billed for diagnosis, they don't get paid for the extra time. So a lot of times you'll see "could not duplicate" and they're on to do the next oil change that comes in the door.
Keep in mind the typical dealer customer is the kind that pays the bill and has no idea what's going on under the hood. It's in the dealers best interest (and arguably the customers) for the dealer to find everything that could be wrong, sell the customer the repairs, and get it done. If you go in for an oil change and 2 weeks later your ball joint starts clunking, you might realize that the two are completely unrelated, but your average driver would often get pissed because "the dealer should have caught it". So when you take the car in to the dealer, expect to get estimates for stuff that really isn't bad yet but may or may not go bad within the next six months or so.
I remember having my '94 at the dealer to get the boot replaced on the steering shaft at the column. I was on my way back to the dealer at the time they said they'd have it ready when I got a call that said "looks like you need a new rack and new outer tie rod ends". I got into the shop, they hadn't touched what i'd brought the car in for. I made the tech show me what was wrong. I had one bad tie rod end boot - "we don't sell just the boot, and you should always do them in pairs". The rack was "a little lazy" (car had probably 125k on it, lazy is fine). So he recommended $1500 in repairs. I told him to do what I brought the car in for, and do it now. The only reason it was at the dealer for that repair was that the flat-rate time was low enough that it wasn't worth doing it myself. But it probably took more than the flat rate time to do the job, so the tech was looking to make some money. Many dealer customers would have said "okay, do it" and paid the bill.