Let me write here an answer from the superuser.com question due to my complete solidarity with the author:
quote from the Ask Metafilter:
The only possible way to make keyword searching efficient over hundreds of terabytes (or whatever their index is up to these days) is to precompute an index of words.
In fact a full regex engine is turing-complete, and you can write arbitrary regexps that will gobble up near infinite amounts of CPU time and memory. For all these reasons it would be technical insanity for them to offer regex searching to the general public.
Update: as it rightfully pointed out, regexp is not Turing Complete. Stay tuned for the more detailed answer:
TBD…