I also wouldn't call it coasting. I think with Pierce, it's just a matter of his shot falling or not. Lately, it hasn't been. But then he would go out and get back-to-back 30-point-games, and everyone would stop worrying.
For me, you get worried about Pierce when he stops getting to the FT line, and he's still doing that. If anything is shutting him down, it's more a matter of the increase in numbers of plays run for Ray (how often of late have we seen Pierce provide a timely pick to free up Ray for a wide open shot? See: GSW, PHI games), and teams focusing on Paint defense thanks largely in part to Rajon Rondo's "sudden" aggressive nature (note how nicely Rondo's coming-out party aligns with Pierce's drop off). Once the jumper starts falling again, though, he'll be fine.