Chris,
Most of the time, you should be able to skip to the bottom; I usually can, and I'm on an ancient, small laptop. ("Ancient" = six years old.
)
Regarding the size of the image(s), I have no control over what the submitters have loaded on their websites. I cannot speak for the APOD guys, but it's easier for me to deal with images submitted by URL than by attachments. Some submitters offer their image in several sizes on their websites; if so, I select what is typically the "small" or "medium" image to display on a thread and then link the image to the largest size available (so clicking on the image will take one to the image website). If the image is available in only one size, that's what goes on a thread (though sometimes I skip putting very large images on a thread; I know people don't like scrolling).
Attachments are a different matter; I have to ask for permission to display them (copyright issue), and if an image is large (most are), I will reduce it to what I think is a reasonable size to display. (For me, clicking on an image with scrollbars expands the image if the image itself is not a link; I hope it works like that for others!) This takes time, space, and limits when I can put an image up.
In the case of the images on this thread, there were no smaller versions; it was post them large (as is) or not at all. I picked posting. Better to have them out there for some to skip and some to view than not at all was my thinking. Was that the right decision? Y'all will have to tell me; maybe I'll start a poll to ask.
If there are better ways to handle this, I'm certainly open to them and would really appreciate the input.