Some other guys will jump in probably with super technical info but the bottom line is that BL (brushless) motors are a LOT more powerful than their brushed counterparts. The small looking motor in the SV27 is as powerful and can rev significantly higher than a 800 sized brushed motor (which looks like a shorty beer can it so huge, and weighs 1 lb).

BL motors are supposed to run cooler because there is less friction from not having brushes (although my BL motor runs hot). They don't require a break in period, they last longer, and they need less maintainence. Oh...and they are more expensive and require a special BL ESC which is also expensive.