The reason you cant put the apps on the SD card is due to security, lets take this for exapmle:
You bought an app and yo uput on your sd card and now you put that sd card in your friends Hero or any other Android phone and now you transfered the app over to him and he did the same to his friend and so on, and you only payed $1.99 for this app and now 20 people have it and the developer lost money, and there are other things that yo uhave take in to account. but this is the biggest one, when i had my Blackberry every app i bought was registered to my PIN so even if i gave my sc card to friend he could not use my apps cause he has a different PIN #, with Android there are no PIN #'s. But there is a way for Android to make it possible to have something of the same instead of the PIN they can use the phone serial # but that will take some work.