Non contact AC voltage detector resistors
The base-emitter current is a fraction of the collector-emitter current, but a non-zero fraction. For a larger collector-emitter current you need a large base-emitter current. The RF energy might be too weak to supply the larger base current required if you were to try and maximize your collector-emitter current in a single stage. 

The 1 megaohm resistor is sized to be small enough so that T1's collector-emitter current can supply reasonable about of base current to T2 is, but large enough so that the base current of T1 does not load down the signal source too much.

The collector resistor for T2 is smaller to allow it to produce more collector-emitter current by taking advantage of the fact that there's a lot more power driving its base.