Always online can be a problem. Diablo 3 on PC was always online, so we got treated to lag spikes while playing single player offline (not framerate drops, but actual Internet lag). Not to mention if the servers and/or your connection go down, you can't play.
I personally never had a problem with the original MS plan for 24 hour check-ins. That is NOT always online. That system allowed for reasonable outages and wouldn't burn you if your connection went down for an hour.
Always online can and does cause problems for users (see the Diablo 3 launch, Sim City launch, etc).
I leave my console plugged in all the time, and my connection works fine, but game servers aren't as reliable. Try playing an EA Sports game on a Friday night during busy hours.
If the game is truly offline, it shouldn't break if there are connection problems. Cheaters are going to find ways to cheat no matter what.