I have to agree. The "two diodes" analogy implies equal amounts of emitter & collector doping, which wouldn't account for why charge carriers are able to diffuse across the base, rather than just in or out of it.
In response to the original question: the NPN and PNP terms refer to the level of semiconductor doping in emitter, base, and collector structures of the transistor. For NPN transistors, the emitter is more negatively-doped than the collector, so it's really more like an (N+)PN transistor. Likewise, the emitter is more positively-doped than the collector for a PNP device...or (P+)NP if you want to look at it that way. On a diagram, the arrow for NPN is "Not Pointing iN," and for PNP it's "Pointing iN Proudly." A little nmemonic there. 8)
One quick & dirty way to test both kinds is to "saturate" the base pin by connecting it to the emitter (maybe through a button) so that the transistor operates on an on/off basis. To test NPN, connect the emitter+base to positive, , and the collector to negative; and if the trans works, you'll get a large amount of current going out of the collector. For PNP, connect emitter+base to negative, and collector to positive.
If you have a mystery transistor, you can **broken link removed** or purchase a full-featured tester that will return an "NPN/PNP" and "PASS/FAIL" output.