Depends what you consider as "Apple being successful". Clone market was peanuts to Apple financially, initially $50 a license. Now they sell you $500 of PC parts jammed into their machines for $1200 (minimum, base model iMac).
It may however have got them more market share vs. MS, but I honestly think Jobs saw the nightmare the early PC users had happen to them with vastly varied hardware and the drivers, IRQ, and etc. problems back in the DOS days. No doubt Jobs was a control freak, but there's something to be said for writing an OS for hardware you are 100% in control of.
I think Apple would have never become the "prestigious" brand that all the hipster fanboys love and all the press worships today if the clone program was kept going.