If Canon does indeed have openings between any glass element on the chip and the chip itself they should explain that and warn against liquid cleaning. It's as simple as that.
Oh, please. We're not in kindergarden, and Canon shouldn't have to tell us every possible way which we should not clean our sensor. Have you noticed that there isn't any instructions not to use microfiber cloth, and not any instructions not to use a vacuum cleaner, and not any instructions not to use a water hose?
But yes, they do put in some
kind of warning.
And here's what Canon writes in the manual for the 20D:
"Note that the image sensor is a very delicate component. If possible, you should have it cleaned by a Canon Service Center."
"4 Clean the image sensor
* Use a rubber blower to carefully blow away any dust, etc., on the surface of the image sensor."
"Use a blower not attached with a brush. A brush can scratch the sensor."
"Never use canned air or gas to clean the sensor. The blowing force can damage the sensor or the spray gas can freeze on the sensor."
I think there are some pretty strong hints here that you shouldn't use anything but ... *tada*
- a rubber blower.
There is no indication
that Canon considers it safe for you to use fluids, and every indication otherwise.
I don't see why Canon should add all sorts of warnings, such as "don't dry your cat in the sensor chamber" (uh, sorry, that was the microwave, wasn't it?). That is completely unnecessary. If people don't understand that they're taking risks by deviating from Canon's instructions, then that's their problem, not Canon's.
Of course, people with experience can sometimes choose to take such risks, because there is a good likelyhood that they will know how to and possess the skill to avoid the dangers.