For terrestrial the situation is similar, but on a much smaller scale. Freeview covers all the SD and HD channels in about 7 multiplexes ( equivalent to transponders in the satellite environment) from Sandy Heath. Well, about 6 and a bit multiplexes if you eliminate the SD equivalents of the BBCs and ITV. ABM tunes to the primary multiplex (PSB1/BBCA) and then uses frequency information stored in the NIT PID to populate the channel information on lamedb without having to tune to all the other multiplexes. It's working for SD, but not (as far as I know) for HD. ABM doesn't work at all well in the Irish DVB-T environment due to duff frequency info held in the NIT.
The E2 scan that you are doing will pull in all the HD and SD channels as you say, but the E2 scan does not seem to use the channel numbers (LCNs) stored in the service information, so you don't get a nicely sorted scan as you would on a commercial Freeview receiver. The advantage with ABM is that it orders the channels. I just do an E2 scan of my local multiplexes and store the services manually in my favourites list. As there are only about 10 TV and 9 radio channels live so far on the Irish DVB-T service it's not a big deal.