The use of a secondary is not a "yes or no" question. Neither is it some sort of "obsolete" process. Yes, the closest thing to a secondary in commercial brewing is probably a "bright tank," which is used to clear the beer. But that answer isn't exhaustive either. Homebrewers are not commercial brewers, and the secondary may be used for a number of reasons, and with specific beers. Some of these things have been outlined in this thread. My list of reasons may or may not apply to kegging. I don't keg, and have no particular interest in it.
As I see it, the following DO apply:
1. As in commercial breweries, to clear the beer.
2. To allow for the time needed for some high gravity / complex beers to mature / age properly. (Again, there is room for argument about whether the bulk aging in a secondary is superior to aging in a bottle or keg; I have no intention of exploring this argument here)
3. To provide an environment for amendments of fruit, extracts, spices, or for dry hopping.
4. To provide for storage pre-bottling, when logistics don't permit it. I have two batches that were put in the secondary two weeks ago, and due to other contingencies, cannot be bottled until the middle of November. These batches had been in the primary buckets for 3 weeks, and I didn't think it expedient to leave them in for another 6.
5. It is true that "secondary fermenter" is probably not a useful term. The only neologism that comes to mind immediately is "booglefratz," which would probably not find general acceptance. Anyone have a suggestion?