By "how many mac clones out there" I assume you mean "not a lot".
Because right now, "hackintosh" are still very very marginal in the big picture. On specialized internet forums it may seem that everybody want to build their own computer and deal with those stuff, but it is a very tiny fraction of users.
About clones and licensing OS X. The thing is, Apple, even with a relatively small fraction of the PC market is in a very desirable position. They don't sell a lot of computers compared to other brand, but they sell a lot of "high end with high margin computers". They are very competitive when you get into the market that sell for 1000$ and more, and this is the market where the margin are very desirables. One big reason for their success is that they offer a "unique" (if not better) experience with OS X. Hardware design is one thing, but OS X is still the thing you use everyday that make people want to move to Mac and pay the price.
Anyway, to make thing simple, they offer with OS X something that nobody else is able to offer in the PC market, so they can remain strong in the medium to high end market segment where the real money is.
Other PC companies (Dell, HP, Lenovo, Toshiba, Sony, ASUS, etc.) all sell almost the same thing, at least in the consumer eyes, which is a machine that run Windows, and they are all able to build relatively good computers hardware. So, in front of relatively similar products, the consumer will most of the time go with the cheapest one. So basically, PC vendors are forced to compete on prices, and competing on price mean leaner margins.
Of course, there are PC that also sell for 1000$ and more, but the problem for any specific vendor is that if you find a good 1500$ ASUS computer, Dell is probably able to build an almost identical product also, Lenovo and others too. So one will cut his margin to sell the same one for 1400$, and the other one for 1380$, etc. Basically, at every level they have to accept smaller margin because they have nothing that differentiate them from the competition.
Apple is the exception, they have OS X. They are different. They can compete on something other than price, and that is gold.