JP rushes just have a bunch of significant weaknesses, and if they do appear on the playing field you have to call it off and go for HA almost definitely - like OCs in the hive, Lerks, bad Hive areas, good Fades or the 2nd Hive being up (which is technically possible - it can be up at about 6 minutes, roughly the same time you'll be decking out JPs).
Heck, the only compelling reason to JP rush is because a) the other side overpowers you on the ground or B) you can't afford to wait the extra 50 seconds to research HA.
But yeah, techrushes work on almost any map fairly well, but best on agora/hera.
Edit :
@rad:
Good players on the marines simply weigh more by themselves, and even if they're being fairly stupid will heavily influence the game and territorial control. In other words, games with good marines are easily recognizable by you having a very easy time moving around and taking ground for the first few minutes - and after that, even the Fades won't save the 1RT/1Hive situation.
The only real counter to it is good teamwork on the Skulk/Gorge side, like only entering camped rooms with at least 1 friend and generally communicating well with the team. But how many people naturally do that?