aqua_holic
Aquarium Advice FINatic
it really is rather simple.
In a smaller volume of water any contaminates are more greatly concentrated and parameters can more quickly and broadly go wrong if something such as a death or power loss of even a couple of hours happens.
Even with an appropriate bio-load, in the event of something like a power loss, a ten gallon will go bad a lot faster and more dramatically than a 100 gallon tank with appropriate bio-load.
That argument easily goes the other way. A smaller volume of water is less susceptible to airborne contamination than a larger volume of water due to the surface area available to receive contaminants.
I lost power for almost 5 days and my small 2.5, 5 and 10 gallon tanks were no worse off than the larger 125s. Not sure why you think that, or exactly what would go so wrong...
Don't take this the wrong way, but to suggest that fish are at risk of death due to the power being out for a couple hours is fear mongering. Yes there are extreme situations where that may happen, but as a general statement that's just not so. Fish spend days in little bags of water when shipped. A few hours with no filter is nothing by comparison.