Bill brings up a key point about file size. It's not only the number of pixels, but the amount of compression that's done to the file. Your camera probably doesn't do any compression, but pretty much all the resizing software available does. Another thing that adds to the file size is the metadata that's included in the photo (but not seen on screen). This metadata includes all sorts of info about the photo: The brand and model of the camera, the f-stop, shutter speed, and other camera settings, the date the photo was taken, and in the case of cell phone photos, it might even show the GPS coordinates of the location where the photo was taken. All of this info adds to the file size. There are ways to remove all that info, but I'm not sure if Pixresizer does it or not. (I use IrfanView, and it does have the option to strip the metadata out of the photo.)
And I concur with Darren. Right now our backup size is pretty substantial, and it can take hours to download a copy of the backup for safekeeping. Steve, I'm guessing the forums where you don't run into file size restrictions are either not making backups of the forum, or they're leaving the backups on the same machine where the forum resides. (Sort of like leaving the only copy of your automobile registration and title inside the car. You're hosed if the car gets stolen or burns.)