According to
AnandTech, the graphics in the higher-end desktop i5 are about even with the AMD 790GX, which, in turn, is roughly
equivalent to nVidia 9400. The mobile i3/i5 has graphics on par with the desktop i3/i5 (other than the highest-end,) which is only
slightly slower than the high-end i5.
Remember, 9400M is now two years old. Yes, there are faster options now, but the integrated graphics in the laptop i3/i5/i7 are roughly equivalent. Any games that run on 9400M will run on "Intel HD Graphics", minus a single-percent frame rate in some games, and even plus a single-percent frame rate in others.
And the latest Intel graphics
do support OpenCL. (They don't support CUDA, but neither does anything from AMD, for that matter, as CUDA is nVidia-specific.
Yes, the GMA 950 that came in the first Mac mini, MacBook, and MacBook Air sucked ass. The next-generation after that (which Apple skipped,) was noticeably better, and the current generation is even better yet. Yes, if nVidia and AMD could make 'integrated graphics' chipsets for the i3/i5/i7, it would likely be noticeably faster than what Intel provides; the Intel graphics
are competitive with the 9400M.
Finally, the notebook i3/i5/i7 have "Turbo Boost" that includes the GPU in its calculations. So the GPU can ramp up in speed if the whole package has enough thermal headroom. Yeah, if you're running SETI@Home on both CPU and GPU, you'll end up with crappy speeds on both; but if you're playing a game that isn't massively CPU-intensive, the GPU will ramp up and provide you with better speed. Likewise, when you're doing video rendering on the CPU, the GPU won't be using much power, so the CPU can ramp up in speed. All staying inside a much lower power envelope than adding the 9400M would.
Don't get me wrong, I don't want to see Intel HD graphics in the MacBook Pro; and would prefer not to see it in the 'plain' MacBook; but for the low-power Air, it fits perfectly.