If you're moving sections around in a spreadsheet or a word processor, would it be more annoying if the copy/paste kept the formatting or stripped the formatting?
I think it depends on your workflow -- I'd tend to assume the receiving end has some formatting, and it would be best if the copied text was fit that formatting, rather than bringing formatting with it. Ultimately though it seems pretty arbitrary, I guess they just went with the default that benefits what they assumed would be the most popular workflow.
I dunno, we should all just use LaTeX to avoid these kinds of issues.