estimation is not an actual. I suppose you know that.
the website you are talking about, estimates the possible worth of the requested url/website with a tld(no subdomains or aliases).
it tells you the possible PROJECTED income, according to the increasing/decreasing rate of data and activity detail on that domain, driven from other partners, they might have with them.
the things are pretty diffrent. ESTIMATED PROJECTION on DRIVEN DATA.
andddd ONE can not object on Estimated Possible/Projected Data.
and personally if you test an unknown or un-popular site or any site that is inactive for a long time. you will notice that the data you are seeing on websiteoutlook.com might be satisfactory at some level.
PS. I prefer to compare the facts on every kind of targeted website. that are not only with high traffic.