A regular save does extra things that can be omitted from saving for web. One of that is to preserve the color index. This is useful for editing again afterwards as it preserves more data of the image. This however adds to the image size. You can also keep it in the save for web, just have to click the check box.
Ugh. And I overslept.
My SC2 stream, bitchz, love goes to Elyaan the Weird and Fantastical Unicorn.All I would ever want and need is a hug.