I believe many of these less expensive systems transmit over a broad 100khz to 1mhz bandwidth or more.
The bandwidth of all the 900Mhz to 2.4Ghz video Tx's is several Mhz. This is to support the FM video signal, which requires at least 4 Mhz for good results.
They would normally rate the current draw in mA not mW.
The comments from BlackWidow AV are true. Most of the low cost video equipment vendors are stating power specs based on current consumption. This inflates the results, often 10X more than comparable RF power. A couple of us have tested the popular 200mW 1.2Ghz systems -- they were putting out as low as 5mW. I got 40mW out of the one I tested. Details:
http://www.rc-cam.com/hk_video.htm
... is the limited range of 2500 ft you talk about directly because the radio's now are narrowband? I've wondered this in a world that seems to try to focus on cheapening things.
Narrowbanding does not reduce range (it actually increases it). I do not think that you will find that decent quality modern 72Mhz R/C Tx's have reduced range. There is even one RPV pilot (cyber-flyer) that uses a stock Futaba transmitter to fly as high as 20K feet.