UPX is usually better than other generic compression utilities. IIRC it actually modifies the executable before compressing it to provide better compression. I think on Windows it reversibly changes relative addresses to absolute addresses so you get better compression rates.

2GiB quotas on home directories is another reason, but explaining it all on hn isn't really a goal of mine. Suffice it to say there are a confluence of issues. As to network compression via ssh say versus compression of the binary, time it you might be surprised at the difference.