FYI - the foster ladies house might have smelled because foster homes rarely
have only one cat they're taking care of (i.e. more
litterboxes/litter/business for fosterer) and she may have been less of a
"cleaning" type housekeeper than you are.
I have regular very large litterbox for 2 large cats; I scoop it whenever I
visit bathroom, use hard-clumping sand-like litter in it. If you scoop
frequently (don't ever scoop the urine clumps down toilet, just the
"offerings" from cats....I dump litter clumps in nearby plastic bag, which
needs to be put in outside garbage frequently)you
should be eliminating whatever causes odors bigtime.
Suggestion: spend your cleaning energy on *cat hair removal* in
house....there is loose fur in here, but it doesn't smell, you gotta vacuum
often. The fewer cats you have the less loose fur around.

Per Beth:

According to an article I read in National Geographic a loooooong time ago, the
sense of smell starts to adapt to odors within 45 minutes.   That suggests that
somebody's home could positively reek of cat smell, yet they wouldn't notice
anything.  

I think I've experienced this myself several times.  The most noteworthy being
back when people were allowed to smoke in the workplace.   Then we'd just get
sort of sick/headachy every afternoon around 2 - but didn't smell that much of
an odor.     Now, when somebody who smokes comes to the cube or steps into the
elevator; between their breath, body odor, and clothing odor it practically
knocks me over.

Also, one of my co-workers dicovered perfume once.  Came to work smelling pretty
nice one day.    Then a few days later, she smelled stronger...and stronger and
stronger until we were all exchanging looks whenever she walked by.   My take
was that her olfactory sense had adapted to the scent day-by-day and she was
unaware - thinking she needed a dab more to get the same smell...