I use to install and service commercial ttwo way radio systems.  I never
saw an advantage to dcs, but often it is something the competition comes
up with.  The idea is that if you once make the sale, say with a
particular dcs plus or minus, the customer will have to go back to you for
repairs and replacement or add on radios.  I lost bids on more than one
occassion when motorola would sell below cost just to get the original
system.  OF course once that was done, they more than made it up on
repairs and the customer would most likely   come back to the original
seller for more radios.  When this stuff firsted started, each company
called their subtones different things,  One was private line, and I
forget the others.  Wer basicly the same thing.  This was before dcs.  At
one time motorola actually used letters on their stuff so they couldn't be
cross referenced.  That is why some charts still list tht tones by number
and a letter designation.

Anyhow, enough rambling I guess.
73s
Butch Bussen
wa0vjr