i asked the same question when i first started my 135... although i included alot of the suggestions (lots of rock, DEEP sand bed, and currently putting in a fuge).. but i did not put on a skimmer....
my reasons were simple.. didnt have the money for a good skimmer (Euro Reef), and i didnt want to waste my money messing with cheepos...
things in my tank have done very well in the short 5 months its been up and running. without a skimmer.... i was adding corals in the third month, and the original corals have grown very well, and all the corals look very healthy and are growing very well.. some are growing at alarmin rates.
I have no idea why but some of my guesses are that since i dont have a skimmer, there is much more organic matter in the water to feed my filter feeders.... but i am still saving for my skimmer of choice.