Are Buck converters conceptually same in low/high power applications?
All switching power converters are conceptually the same - they contains some energy accumulating devices - inductor(s) and capacitor(s) and controlled switch that commutate the input energy, switching it ON and OFF.

The big difference between different kinds of switching converters (buck, boost, etc.) is the topology of the elements.

While the different power inductors and capacitors are generally the same, for the switch different elements have to used. There are thyrsitors, BJTs, MOSFETs, IGBTs. In the old times even mechanical switches has been used. 

Of course, the auxiliary electronics (the control schematic, feedback regulator, protections, etc.) highly vary depending on the output power and the destination of the converter. And it is obvious, that on high power schematics, all these auxiliary modules tend to be much more complex than in the low power converters.