Yes, because of MLB rules, MASN is the only place to see live Nationals games in this region. Everything else is blacked out because MASN is paying $26 million for the exclusive TV rights. That's the only reason for the blackout. You will see every Nationals game, either home or away, on MASN, regardless of stadium attendance.
The only exceptions are Saturday games on FOX and Sunday on ESPN. they are exclusive nationally, so MASN would not have the rights to show these games.
I live in Richmond, and on channel 43, Comcast says "MASN 1, LAUNCHING APRIL 1". MASN2 will be on channel 19. Cox is launching the channels in Hampton Roads on 3-27.