No.
Reason? Starcraft maps are small (in the kilobyte range) which took seconds to download via dial-up (56k) for people in the same server (region) as you. This is a short time for downloader and not much stress on the connection of the uploader.
osu! map packages are usually around five megabytes each. Many different regions play osu!, and the upload-to-download ratio is smaller than it was back then. The upload would be stressed for many players, which isn't good because shouldn't be stressed on Internet connections.
Also, like with illegal torrenting, you're likely sending copyrighted content to other people, which is usually more annoying than downloading it for ISP's.
Requires port forwarding for naive methods. This can be worked around, though.
peppy probably wants people to donate to get quick access to maps. He could hand everyone osu!direct, but then he'd get less donations. He could implement this, but then he'd get less people using osu!direct.
Requires an option to disable and another to cap, for both upload and download. (Cap and enabler can be combined, likely.)
Requires a cancel button to stop downloading if the download is too slow, so the user can go to the web download.
Yes.
Reduces the load on the osu! download servers. Quick and relatively simple to implement. Verification is simple. Convenient. Less alt-tabbing for fullscreen players (like me) which slow down the computer.
Can't think of much else. =]
I'm leaning toward No.
Also, doesn't Starcraft download from the host only? That's how WC3 works.