Real life laboratory data has confirmed this fact (i.e., "Also be aware that the most IBUs any beer can have is about 90 IBUs") repeatedly for ANY beer, except perhaps for those cheating by adding hop extracts and special engineered techniques to pump more IBUs in. But for anyone using regular hops in a conventional manner in the boil or the whirlpool or whatever, the maximum limit of solubility of the isomerized alpha acids in normal beer is about 90 IBUs. Following is a little bit of supporting data and discussions for you. I'll agree with you that the amount of data published on the web appears scarce; either that, or we just don't know all the right technical terms to search on. And yes, it's highly technical, so if you're not a hop scientist (I am not), then it's not easy to find real data. What we hear is substantiated by dozens of independent sources though, and from people who've been on the direct receiving end of scientific presentations, etc.
http://www.basicbrewing.com/index.php?page=basic-brewing-radio-2011
http://traffic.libsyn.com/basicbrewing/IBUBrewingExperiment.pdf
http://traffic.libsyn.com/basicbrewing/IBUFollow-up082311.pdf
https://www.homebrewtalk.com/showthread.php?t=273482&page=2
http://aussiehomebrewer.com/topic/43211-worlds-bitterest-beer/
The IBU ceiling thing is true. Believe it. Or don't. My toe hair will continue to exist either way.