You're absolutely right, it is linked to the specs of the computers involved. But frankly, I think you may be underestimating just how many calculations are involved here; the fact is computing power progresses at a shockingly predictable rate, and short of mathematical breakthroughs, the things stated here can be taken as reliable information (2048-bit keys being pretty secure for awhile, 4096-bit keys being secure for many years to come).If you actually get into computer science and analysis of algorithms, you don't stop and preface everything with "all time estimates are using my home first generation Pentium, please read on..." or something. You say it takes N calculations on average, or N calculations in the best case, or N in the worst case, or some other estimate that applies to a situation. It's up to the person who wants to get a feel for that number to translate that into a time frame on a given system; basically I'm saying these are typical answers and they aren't really leaving details out so much as ignoring them because they're meaningless for the subject at hand. Besides... most people find this stuff dry enough as it is without starting to throw in algorithmic jargon.