there is a plugin that i just found that will do this with the gallery in 2.5 goto wordpress.com and search plugins for image and look. i downloaded like 20 diff ones few days ago and dont remember which one it was.
No wordpress doens't do that, but with a little piece of javascript you can resize all 'content' images to a fixed size
i have a script i resize images using, and it keeps the aspect ratio of the image in tact as well, pm me for it, its free =]
I'm pretty sure it does, when you're making a new post and you select to insert an image. It only resizes it to preset values, something like 50% and then thumbnail size.