It's not about storage. It's the display width that is easily settable when you add a pic. I have no idea why 640 was picked, but it's not my place or your place to tell someone else how to run their website. Fyi, the pic above makes it impossible to read without scrolling on the system I'm on at the moment. Not exactly reader friendly.
Finally, this isn't the trip report website although some of you prefer that part of the posts. There are lots of places that prefer that content. I suggest it would be easier to post there and link to that post here instead of trying to change the rules here to suit your blogs.
There is a blog part of rv.net. No, I don't know the address because it's not that interesting to me. If you like that content, go there. It will be more of what you are looking for.