liteswap
Well the differences between a Cessna 152 and a B747 are many - however one particuarly relevant here is that the B747 (being a large public transport airliner) is certified under performance category A.
That is to say, that if an engine fails on the take off roll, you must stop if you are before 'V1', and continue into the air if you are beyond 'V1'. The aircraft is certified as such that either course of action should lead to the aircraft still being controllable by the pilots.
In a Cessna, if your engine fails on take off you are going down. In a Class A aircraft, your remaining engines will meet thew climb requirements. In the case of a reduced thrust take-off, you may reach V1 at a different place on the runway, however the aircraft will still meet all the safety criteria of it's certification. A reduced thrust take off is standard in all airlines that I know of, with certain parameters where full power takeoffs are mandatory (first flight of day, every 10th flight, Anti-ice on etc etc). I will be taking off later on today with about 80% power.
*V1 = take off decision speed. Above V1 = GO, below V1 = STOP. At certification, this is the speed at which the critical engine is assumed to fail.