I'm guessing that lagers at 50 degrees ambient are less likely to drive the temp much beyond 50, when compared to ale yeasts sitting at 72 ambient pushing that ferment past 72, all else being equal. No data or science to support that, just my wag at this point.
This same question has really been bugging me over the last year, so I recently installed a thermothingy on my plastic bucket fermenter. In two lager ferments sitting in a controlled fridge in the basement, neither batch got more than 2.5 degrees above the current fridge temp at any point in fermentation (ferm temps 48 - 51 at all times). This was measured on one NIST certified thermometer, and one calibrated to that one. The probe was sitting at the 3.3 gallon mark in a five gallon batch, almost dead center of the bucket. The controller was not attached to the fermenter internal probe.
I'd expect that an ale fermentation at 72 is significantly more exothermic due to the higher metabolism, and that the heat can't be dissipated as quickly. Of course, there are other factors: OG, fermenter geometry and material,...
oh jeez, it's almost new year's. how ironic that a hobby that makes you a sure invite to parties is also the same hobby that can drive you into a trappist monk-scientist mode. Happy New Year! I'm off.