Really, its a simple matter of engineering and cost. I own the 2012 i7 mini and I can tell you it runs plenty hot. The CPU itself runs at 45 watts at 105ºC max. Probably near the limit of the Mini's power supply. The new quad core haswell (the same chip in the retina macbook) maxes out at 47 watts and needs to run 5ºC cooler. To use that chip they would need to augment the power supply and cooling which would require a case redesign. Also, the package size is different. The quad haswell is larger and requires a different BGA grid and heat sink design. Larger chips are also more expensive to produce and its very likely Apple can't get the Haswell quad i7 as cheaply as the previous generation. It's likely that Apple considered their options and decided to go with a cheaper Mini rather than spend extra R&D to redesign a Mini that could likely be more expensive to produce. The i5 used in their mid tier configuration has much higher performance PER CORE that the previous i7, so for most apps it will actually be faster. This diminishes the benefit of the i7 quad in many cases. It just sucks for parallelized CPU only tasks like video encoding, rendering, etc. Which will be about 35% slower in my opinion however the faster GPU could pick up some slack. Heavy multitasking will suffer as well. Benchmarks will tell the story better.