I really don't know the real reason behind why its hard to get things rolling on the Epic.. I don't think it has anything to do with the lack of devs in the past.. We have had some great names with a lot of talent that worked on the Epic 4g. Some will disagree with me on that point and say how HTC has had better devs, I don't really think its that HTC or other devices have better devs its just those devices are easier to work with for whatever reasons.
I've heard of people taking roms from one HTC device, and having them work with little to no changes on another htc device. Either their kernels are built to adapt to more variables (like how a linux live cd works on a LOT of computers). So once they get things rolling on one, getting past the locked bootloaders and such, it's all smooth going from there.
Samsung seems to highly optimize the kernel to the specific hardware. This is exasperated with the Epic having a keyboard, notification light and camera flash, that I suspect causes a hang in other kernels when they find and can't identify the hardware and other slider related items.