Let's see... apparently it's not that uncommon.
The 76ers, Lakers, Bulls, Mavs, Blazers, and Jazz all have the five current starters averaging double figures.
For the Spurs specifically, we've had five players average double figures in 2010-11 (three starters, two reserves) and 09-10 (three starters, two reserves). Never before, dating back to 98-99.
Here's the detailed look -- I noted specifically players that were injured for a notable portion or who were acquired via trade, since that elevates the averages of other players on the roster.
The 76ers have six players averaging double-figures, all five starters and injured Jason Richardson (likely, if Richardson wasn't injured, only five would be in double figures).
The Spurs, of course, have six players in double-figures -- all five starters plus Ginobili.
The Clippers have five players averaging double-figures, but two -- Matt Barnes and Jamal Crawford -- are reserves.
Warriors have five, two as reserves (Jack and Landry).
Knicks have five, but one is the injured Stoudemire.
Bucks have five, two as reserves (Dunleavy, Redick).
Cavaliers have eight(!), one injured (Varejao), one joined halfway through the season (Speights), and looks like two of them are bench players.
Lakers have five, all five starters.
Kings have five, one as a reserve (Thornton).
Timberwolves have seven, two injured most of the season and one a reserve (Barea).
Hawks have five, one injured (Lou Williams).
Bulls have six, all five starters plus Hamilton.
Celtics have five, two (Terry and Green) as reserves.
Raptors have seven, one trade acquisition (Gay), one trade loss (Calderon), one injured (Bargnani), one reserve (Anderson).
Pistons have five, one trade loss (Prince) and one trade acquisition (Calderon).
Magic have six, two injured (Harris and Davis), one trade loss (Redick).
Bobcats have six, one injured (Sessions), one reserve (Gordon), one whatever-Pargo-is.
Nuggets have six, one injured (Chandler), one reserve (Brewer).
Rockets have six, one trade loss (Patterson), one reserve (Delfino).
Mavs have six, one reserve (Carter). Nowitzki was injured a while, though, bumping up the others' averages.
Blazers have five, all five starters.
Suns have six, two reserves (Beasley and Brown).
Jazz have five, all five starters (Williams out a while, though).
Hornets have five, one reserve (Anderson).