Ipod Itouch IPA question

i have a question. just like you can download music why cant it be the same with IPAs?
like..not cracked or anything. if i downloaded a game from itunes on my desktop. and uploaded the file so others could download it, it would work right? or am i wrong?
Answer #1
for a piece of software to run on an ipod (any ipod) it must be digitly signed by apple, and for them to sign it, you must submit it to the app store