[Will]

I don't know what UI you're talking about. For me, all I have to do to classify something as spam is check the box next to the message (or use k/j to move up and down the list, and x to select, for the times when I don't feel like using the mouse). Then it's as simple as clicking the "Report Spam" button right at the top.

As for permanently deleting a non-spam message, that's a little harder. The main reason is probably because gmail is supposed to be centered on search, so you archive (y key) any messages that aren't current/important, then search for it later if you need it.

For example, in my account, Gmail says I have 1280 conversations when I go to the All Mail section. My inbox has 5 conversations (summer internship, work on a friend's campaign website, interview with microsoft employee, application to be RA at my university, and a recipie from my mom). Starred conversations (for me, this simply is an importance flag) has five conversations (two also in inbox).