I think one of the primary reasons for this is the comparative strengths of the controllers. I love the 360 controller and think it is the best that I have ever used. It's not perfect - the d-pad is poor - but it is streets ahead of PS3's Dual Shock 3, with its horribly spongy analogue sticks and its lack of proper triggers.
Fortunately for me Power A has brought out a PS3 controller that benefits from the same button/stick layout as the 360 pad - the Power A Pro Elite Wireless Controller. I don't normally like third-party console peripherals, as I find their build quality is not up to the standard of their first-party competition. I only tend to buy them if they have features that the official pad lacks - the last third-party pad I bought was a Logic 3 wireless pad on the original Xbox (at the time I was sharing my house with a baby that liked to chew everything).
Clearly this pad does offer something different. The first thing that you notice when placing it and the official pad side by side are the asymmetrical sticks. The Dual Shock's sticks are, essentially, in the same position as when first introduced onto Sony's system, with the short-lived but excellent Dual Analogue Controller for the original PlayStation in 1997, which was presumably influenced by the layout of the original, stick-free PlayStation pad.
As anyone that has spent a lot of time playing with a 360 pad knows, having the left stick in the upper left quadrant of the pad is a natural fit with how your hand rests when gripping the controller. On an official PS3 pad, this space is taken up with the little-used these days D-pad. The sticks themselves offer slightly more resistance than the official PS3 pad and are therefore less spongy but are still not as 'stiff' as with the 360 pad. The tips of the sticks are concave (as with the Dual Analogue of long-ago), rather than the convex of the Dual Shock, which I find more comfortable. All in all, I much prefer how the Pro Elite's sticks feel while gaming, when compared to the official PS3 pad.
Cosmetically, the Pro Elite is all black but the fascia buttons are lit by a red light when turned on. I think having coloured on buttons is preferable but it makes little difference in play. The pad is wireless, 'connecting' to a receiver plugged into one of the PS3's USB ports (much like the Wavebird does with a Gamecube). I have found no problems of responsiveness when using the pad, nor have I any complaints regarding the build quality - it seems sturdy enough, if not quite as heavy as the Dual Shock 3.
The handgrips of the Pro Elite are textured to maintain grip. I'm not a fan of this approach - I'm using it to play games while sat on my sofa, not jumping around the room, as with the Wii - and much prefer the smooth look/feel of both the 360 and PS3 pads. It isn't uncomfortable, just unnecessary.
Look at that hand - never done a proper day's work in its life
One area that Power A hasn't followed the 360 design on (fortunately), is with the Pro Elite's d-pad. Rather than the 360 pad's ill-defined 'wheel' deign, Power A has gone with an old-school, SNES-style cross, which is as good as the PS3's and far better than the 360's.
Another major failing with the official Dual Shock 3, is with its L2 and R2 shoulder buttons, which are regularly called upon in games to act as triggers, a task they are singularly unsuited for, particularly when compared to the actual triggers on the 360 pad. The problem is that the buttons are convex, making it easy for trigger fingers to slip off in play (or at rest). Game (and other retailers) sell small plastic veneers to place over the L2 and R2 buttons to make them feel more like triggers and these work well. The Pro Elite's L2 and R2 buttons have a concave design, making it easier to rest fingers on them in play, a big improvement on the official pad.
I always get concave and convex mixed up. These are concave, hopefully
I think what my appreciation of the Pro Elite shows is that Sony has missed a trick with redesigning the outward look of its pads in the move to this generation, as Microsoft did with the move to 360 and Nintendo always does when upgrading its hardware. While the tech on the inside the official PS3 pad has changed a lot since 1997, the outward design and fascia placement is essentially the same, which is disappointing and shows a lack of ambition.
I paid £30 for the Pro Elite , which I think is reasonable value. I did see it £10 cheaper in the Amazon January sale but procrastinated and by the time I'd made the decision to buy it had returned to its original price. If you're unsure about making a purchase, it might be worthwhile to await the next batch of sales and then go bargain hunting - £20 for this pad is exceptional value.