Or it's possible that Intel just decided to skip certain parts of hardware security systems in order to squeeze some more per-cycle performance, hoping that nobody would notice these holes. Well, someone did notice, and this will bite them at some point (if it hadn't done so already, look at how much of the market AMD took back recently).
I'm also kinda wondering about the performance hits of these software fixes. One after another, these holes will get found out and this will grind down performance of their chips - even if every of these fixes will bring marginal decrease, it will be very noticeable when these pile up.
Also, I've heard - I think from one of recent Gamer Meld videos - that Macs will have to disable hyperthreading to ensure safety, and we already know what does it do with performance.