If any of them want to listen to music with legitimate headphones, they have to buy adapters to fit the intentionally-small opening. It's the same for all their proprietary plugs and devices. They exclude other RAM and hardware manufacturers from their desktop, even those that produce better products at a cheaper price.
The RAM statement is false.
The "even even those that produce better products at a cheaper price" statement is a matter of opinion. As a side note, I'm afraid it's an opinion that few people share. There are a lot of points where you can pick on Apple; industrial design is not a good place to start. (It's kind of like going after Benjamin Franklin for being a crappy politician, instead of say slave ownership or smoking pot. Industrial design may be what Apple is best at.)
They do exclude other computer makers from shipping computers running their OS. A lot of companies do this, though; the only reason it seems weird of Apple is that Microsoft doesn't do this and competitors are so small that it's basically dual market. There are other examples, though: you can't port the software running a Texas Instruments calculator or Mercedes Benz' iDrive control system anywhere else. But I'm not sure it's an abuse of power, it's just proprietary software. Go Linux if you want more freedom.
I've also bought plenty of cheap RAM and hard drives for Apple products. Just bought a Seagate hard drive for a MacBook last week. Apple doesn't manufacture their own hard drives.
The contacts were all standard, but most existing cables had big clunky molded plastic plugs that wouldn't fit past the case to fully engage. The iPhone case was redesigned in 2008 and no longer required the recessed jack.
It's all tradeoffs. Extending the jack would have had it protrude past the semicircular profile of the case, that would make a lump and spoil the look and feel.
So every time you notice that your new headphones no longer have a giant molded lump on the end of the cord to make it look like a serious 1970's 1/4" jack, you can thank us 2007 iPhone purchasers. It's ok, I can wait.