I see alot of posts on this forum like this and am curious why they do it.
 
I see threads Labeled, Gen 1 problem, Gen 3 problem. Gen 3 body parts for sale. Gen 2 this and that. and then you get into the thread start reading through it and its about an SW20. Now I honestly don't know the ins and outs of an SW20, I have chosen to steer clear, but I do know lots about AW11's and ZZW30's. so when I see people having issues with their "Gen3" I try and give them a hand only to realise. I have no idea what they are on about.
 
Why are SW20's refered to as Gen1, Gen2, Gen3.
 
a Gen1 MR2 is an AW11, a Gen2 MR2 is an SW20 and a Gen3 MR2 is a ZZW30.
 
http://en.wikipedia.org/wiki/Toyota_MR2
 
Can anyone point out the roots of this odd phenomenon?

SW20 'Gens' refer to the revisions of that particular model. I'm not sure where the 'gen' tag came from, most Australian cars tend to use the 'series' label, so you could have a AU Falcon series II for example.
 
Most of the time these different series or generations feature changes by the manufacturer, both cosmetically and under the hood.

They really should be labelled Rev 1 thru 5 in my opinion

yeah I figured that they refer to the different "series" or "facelifts" of the car.
 
But these are still mid generational changes. the "generation" of the SW20 is 2. If every different "revision", "series", "facelift" of the MR2 was a differant generation of the MR2 the ZZW30 is Generation 6 by those standards.
 
  But we all know there was only 3 generations of the MR2 released by toyota's standards. is that correct or is there actually 7 or more generations or the Toyota MR2? 
 
 

Revisions relates to the chassis, gen relates to the motor they came with.

Rev1-2 had gen 2 3sg(t)e

Rev 3-5 had gen3 and beams.

Other forums call the different mr2's by mk/mark.

Mk1 is aw11
Mk2 is sw20
Mk3 is zzw30

What just ace_said 

Basically what justace said.  Gen's refer to the engine revision, rev refers to the chassis revision.

People are mainly talking reference to engine issues. Technically Gen1 3SGTE was never fitted on MR2's only ST165 GT4s.

It's certainly confusing/wrong but:

Gen1 - early model Gen2 engined
Gen2 - revised Gen2 engine (diff tb inlet & revised tranny)
Gen3 - 94+ that everyone knows & loves
Gen4 - Wagon Caldina engine never on MR2

Obviously over the years and mostly being an sw20 owners forum it was alot easier just saying your gen1 etc car, where now there are all 3 generation owners and people keep referring still like the old days it does become very confusing especially when they put it in thread names or items for sale cause obviously i see gen 3 and think of an MR2 spyder but no :( so you can see the confusion lol