Probably an engineering constraint that drove this awful experience. I do stuff in my browsers. Shutting them down means losing context on up to 10 different items I'm working on in a given day. Adobe used to have this problem a lot; they seem to have gotten better at it in the past couple of years.
Probably due to DRM and RIAA / MPAA paranoia. My work on the YouTube Content Manager exposed me to the intricacies of how media companies think about copyright, and the complex rules that can govern what we think of as a single song or TV show. Most of what sucks about iTunes is, I'm guessing, the result of terrified media execs forcing Apple to modify the right UE (effortless, invisible, seamless syncing of all my devices) to make it difficult or impossible to engage in widespread piracy.
C'mon. I am one of your best customers. I have 2 MBPs (personal and work), an iPad, an iPhone, an AppleTV, a TimeCapsule, a shuffle (for the gym) and an older iPod (full media library for longer trips; + backup). It makes me batty that keeping these devices synced is so fraught with annoyances.