A lot of people I know, especially students, use mobile Internet (3G, HSDPA, etc.) Even in a good signal area, they have occasional drop-outs. DSL is also prone to drop-outs, such as when using a bad or improperly fitted DSL filter. Lights and appliances turning on/off can cause the DSL connection to lose sync, especially with long runs from the exchange.
In my opinion, the worse the DRM gets, the more it will encourage piracy and I wouldn't be surprised if some paying customers end up obtaining a pirated copy just so they can play offline and use their purchased version for online multiplayer use. The entertainment industries seem to forget that pirated material has the DRM defeated, so it's generally only the genuine paying customers that actually get affected by DRM.
If anyone can think of a better abbreviation for DRM to describe it as unfair, see this thread.