Interesting and strange at the same time. I was listening on Talksport, and they took a different tack altogether. They summarised it well by saying West Ham had been 'sucked' back into the relegation battle.
I'd say past form does count a lot. Occassionally a team will have a near miraculous escape but for the most part that will not happen. If past form truly counted for nothing then the bookies would have to look at the odds in a completely different manner.
It's just a case of likelihood as you said. Southampton have managed only 9 points in their last ten games, Swansea only 6 from ten, so the thought that they will both achieve 7 from 3 is unlikely to say the least.