I'll try and answer some of those, though you should look up a thread in the HIV prevention forum on "cunnilingus" from 11/03/2006. It's very informative.
Firstly, HIV doesn't survive well outside our cells, so yes, any sort of drying tends to kill it.
Secondly, there seems to be molecules in saliva that inactivate HIV anyway, so there are very low levels of active HIV virus in saliva. Thus the virtually zero risk of transmission from a person givng oral sex, but the slightly higher risk of transmission from the person receiving it.
I'm not sure about why transmission to heterosexual males is harder, but it may be because the high concentrations of HIV tend to be in the vaginal fluids at the cervicouterine interface.
Also, for men, if no sores are on the shaft, infected vaginal fluids would have to get into the eurethra and a tear in there to get into the blood stream. That's the great thing about rubbers: if they don't pop or slip totally off, you're going to be fine. Shaken, but HIV negative.
Thank you WorriedT, Xhost, Monkeyflower, Teak and others please chime in.
It's more difficult from woman to man because of the fact that the mucous membrane in a man covers a much smaller area. HIV does not have to go down your urethra to infect, it can also pass through any mucus membrane that contains dentridic cells which are found in the lining of the urethra as well as in the skin that comprises the foreskin. Also generally speaking a man's semen has a higher concentration of virus than vaginal secretions, the semen is effectively "injected" into the woman and it tends to stay there for a longer timespan.
It has very little to do with cuts on the penis etc.
So explain to me why infected saliva can't penetrate this mucas membrane.
Saliva has HIV inhibiting factors which breaks down HIV to a level that can no longer infect.