I've noticed that the pixel resolution of submissions to LuLa "User Critiques" vary a lot. In a quick check, I noticed many were from 800 to 1000 px on the maximum side, up to what appear to be full-resolution of the original such as 4000x3000.
I attempted to find a "sticky topic" that addressed this issue, but I didn't find one. Perhaps I didn't look hard enough?
Many websites do have limitations on resolution, typically 1024 on the longest side. IMO, this is a relic of years past as far as technical issues of bandwidth and storage are concerned.
However, I can see the purpose of a rather limited maximum, as this can put greater emphasis on composition that "survives" drastic down-sampling. It certainly cuts way down on "pixel peeping" ... if not eliminating.