Microsoft's Aaron Greenberg claimed that the lack of a Blu-ray drive was a key reason why the Xbox 360 has been more successful in hardware sales than the PS3, so far.

While this sounds a little suspect, it does make some sense. He stated:

"Being $100 cheaper is part of the reason we're nearly twice their installed base."

Greenberg also said in an interview with Edge magazine that:

"Sony bet on the physical disc, and there are costs associated with that,"

"The fact that we're able to offer a console starting at $199 is a benefit of not being burdened with that cost."

He also went on to say:

"For us, our bet was on digital distribution, that was the future - the ability to [play] 1080p movies with no disc, no download required; we have the largest movie and TV library, the largest HD library of any console."

Though I do think a lower cost does allow them to push out some more systems, it should be noted that the Xbox 360 did have about a one year head start on the PS3. Even so, I think that the fantastic online experience, and a decent number of intriguing exclusives were the key reasons that the Xbox 360 started off well and is still doing so.

And also, we can't forget that the Xbox 360's infamous "problems" have probably sold a few extra units.  I know I bought another one for that reason.

Source: CVG