Limitation is imposed by the storage space available in the gateway. This may be expanded now that Google Power Meter core is going to be removed from the firmware. But another reason is because an average home really wont have that many large loads that some one may want to track. AC and Water heater are two main (ac being 2 devices actually so that's 3) the other two are extra to monitor something specific that you may have in your house. For smaller loads there is too much of chance for false trigger. For example there is no way to tell if you that 100watt profile you made for a toaster is not going to be triggered by the hairdryer your daughter/wife uses in the morning.
