Petz, Re: It lists the 500m as having "optional Centrino technology, whatever that means
It means that you can get it with Intel's wireless 802.11b solution (which makes it Centrino), or Dell's 802.11g solution (which does not make it Centrino).
Re: Given that the lower cost Inspiron series probably outsells the Latitudes by 2:1
It may very well be the other way around. Dell has quite a large share of the corporate laptop market.