The exclusion of the cent symbol on standard keyboards is somewhat puzzling. All of the typewriters I remember seeing when they were still current had cent keys on them.
Although using the $ and a decimal point certainly conveys the same information, it seems that a cent key would still be handy. Especially opposed to say, a tilde key. Outside of Unix, I never ever have used a tilde in my life.
I guess this could all be written down to a random process operating on its own feedback. That is, for whatever reason, they started building keyboards without cent keys on them, and then using the replaced symbol (for example, the @ key to mean things that it had previously not meant. After a while, usage of the tilde the at symbol and the grave become important parts of computer usage, while the cent key is totally ignored.
However, it still seems odd to me that in a keyboard that has over a hundred keys, and has many keys twice, they couldn't find room for a cent key.