All of them. When the Mac first came out, long long ago, Dearly Beloved, they had a development package you had to buy if you wanted to develop for the Mac. The IBM PC, as inferior as its UI was, had free tools, and soon had actual compilers (!).

As a result, the Mac's toolset essentially consisted of whatever Apple had written, for a couple of years, while development for the PC exploded instantaneously and you could do anything at all with it -- even if it looked like crap, you could actually do what you wanted, and soon enough, Windows came out and it looked less like crap.

Jobs has just barely learned the lesson of 1983. There are lots of apps available for the iPhone and iPad. What he hasn't learned is the larger lesson, which is that owning an entire market might be lucrative in the short term, but in the longer term it won't work.