In the current Arena setting, it's all about burst damage, with matches lasting nowhere near as long as they used to back before Wrath of the Lich King. Ghostcrawler pops over the forums to talk a little about Resilience and how Blizzard feels that it still makes, or will make, a difference. He explains that the reason so many players are wearing PvE gear to PvP is because its readily available, going so far as to call Naxxramas gear the new welfare epics. He says that as more players get Resilience, other players will have to keep pace.
That might take some time. Like I mentioned, even with a complete set of Deadly Gladiator gear and non-set items, it's going to be impossible to hit the Resilience cap. Resilience makes very little impact in PvP encounters right now that the risk to using PvE gear over PvP gear is minimal. Hitting 600-700 Resilience is very possible with a decent complement of PvP gear, but this only reduces damage from crits by about 17% at best. Resilience in its current design does nothing to reduce normal, or non-crit damage. Until more Resilience shows up in PvP gear or its coefficients or ratios changed, the trend of using a lot of PvE gear will probably continue throughout Season 5.