I think the style of play is huge. Wenger likes players who are comfortable in possession and that sometimes translates into inviting tackles. Jack Wilshire's problems seem to stem almost entirely from hanging onto the ball instead of passing, then taking the hit.
Every team knows what to do against Arsenal because they never vary anything about their play. No team in the league is going to out-flare them but it is possible to rough up certain players and break their flow. This doesn't account for the muscle strains, however.
Sanchez, however, was stupidity. Much like Ramsey, Wenger has rolled the dice and overplayed him. Had Chris Coleman not given him a public dressing down last time, Wenger would probably be blaming Chile for his woes.
BTW, it could be that Chelsea aren't picking up injuries because they went for a quarter of a season without really playing. Last season, using a similarly small playing squad, they did lose their intensity two thirds into the season, though (albeit after having done enough to win it). Mourinho is much more tactically adaptable than Wenger and can set up for solidity. Wenger only knows swash-buckling.