Yes, their IQ's are relative... And yes, cats definitely understand doors a whole lot better than dogs. But try pointing to a spot where you want the cat to go and see where that get's you... Or calling one by name to come to you. Or telling it to stop doing something and having it comply. Or catching a treat in mid air... Or taking a walk with a cat off-leash and having it stay by you!
Then there's this: Our very old little mini poodle Sparky did me one better by going completely deaf in his aging process. But he's figured out (or just instinctly understands?) some broad sign language. For instance once you get eye contact with him he knows and complys with the universal hand wave to "come follow me", plus a sign for stop or stay (or 'down'!), plus one for "NO!", and yet another double hand wave sign for "that's all for now, there ain't no more."
Try doing any of this stuff with our big and mean ol' cat Mrs Katz and she'll just stare dumbly at you, probably wondering why we're doing the Lindy Hop in her face!

-But then try to get some privacy in the bathroom? Sheeeesh! -Unless the door is tightly latched, SCRATCH-CLAW-BAM!!, she's right in there with you!
And so my days of blissfully reading
Bass Player magazine peacefully alone on the throne are now gone forever!!

Regards,
Greywoulf