I think more and more top clubs are looking for that 360 degree centre forward, who can drop back into the buildup, play with his back to goal, hold up the ball, and be a predator who bangs them in. With the different challenge of the CL (especially away from home), a team can't get away with a more limited player up top alone.
Giroud has shown some promise for Arsenal, but he's nowhere near the complete player that Van Persie was for us. Besides the goals, the fact that Van Persie perfectly fit the Arsenal system is what made him such a huge loss. We've now got to play to Giroud's strengths (which we've started to do), rather than at the start of the season where it felt as if the rest of the team expected him to contribute the same as RVP did from that position (even if at a lower level).