Agreed on both, but lately not only the MIPS values count for CPU's - as you said yourself, the maths behind games and applications got a little bit more complex throughout the years and floating point operations are especially important, so it's worth to actually consider both.I only put Ghz in the example to emphasise the point. What's actually important in CPUs is IPS (Instructions per Second, iirc) which is a truer measure of processing strength (e.g. comparing the IPS of Pentium D and Sandy Bridge Core i5 shows a huge improvement... the same can be seen with Intel over AMD). Ghz do matter, but not as much as marketing makes you think. For graphics cards, I think it was FLOPS that matter (I remember seeing the 4870X2 advertised for having 1.6 teraFLOPS or something).
Also, there ARE games that run better on quad core (and I think there were some that can actually make use of hexacore or HyperThreading) but they are still rare.
There are CPU's out there that deal with alot of standard instructions per second but just happen to be sloppy with Floating Point operations which causes slow-downs whenever they cannot be (for whatever reason) assigned to the GPU which would usually deal with them as it's designed for it.