what is battery capacity (derating) when discharged in 15 minutes?

[jeepster_apc]

Most UPS that I have seen use 12 volt 7.2 Ah SLA batteries. I looked up specs for two brands, and they say the 7.2 Ah is for 20 hour discharge. If you drain it in 1 hour, it is only worth 4 Ah.
That is 56% of nominal capacity.
Now most UPS also state you get 15 minutes at maximum rated power. So if you suck the life out of a battery in only 15 minutes, what do you get? Less than 50% of rated Ah?