You can't play doubles with all 4 human players...but you can them with 2 human players, one in each team
So thats why its not so appealing to have double tournaments.
So we are stick on the singles until manutoo (if ever) make doubles with 4 Human players.
About second part of your post...y you can be part of TEtour community as soon as new season starts.
Rank: 2008 (5), 2009 (16), 2010 (6)
Results 2010: Singles (70-27), Doubles (56-19)
Titles 2010: Davis Cup, Valencia (s), Eastbourne (d), Zagreb (d), Paris (d)
Final 2010: 10 (US Open (s), Wimbledon (d), Madrid (d), WTF London (d)...)