Thing is they beat Man City away and are capable of beating the top sides, so they can afford slip ups, not great results but they're still top at the mo (also didn't they have 39 shots on goal against West Ham, so they were somewhat unfortunate not to win that).
At home you'd expect us to beat Sunderland, so if we hadn't it would have been a very poor result indeed. If we were capable of beating the top teams then maybe a slip up hear and there (away not at home) would be more acceptable as we'd know we could make it up when we played the other sides near us, the problem is we don't seem to be able to beat those teams.