I'm not saying there isn't a marketing game going on with many or all of the game improvement irons, but I think there is a technology component, and I think you see it in two ways:
One, technology is making clubs easier to hit. If all manufacturers did was strengthen lofts, they would have difficulty selling clubs because buyers would recognize that while they can hit their scoring irons further, they're having increasing difficulty hitting their long irons (e.g., while its great I can hit my 9-iron further than I used to, my 5-iron is now as difficult to hit as my old set's 3-iron... these clubs suck!).
Two, ball, shaft and head changes are producing higher ball speeds and higher launch angles per the same loft head than equipment 30 years ago. Remember a golf shot is not just distance, but also trajectory and spin. If the ball comes off hotter and higher than 30 years ago and they didn't compensate by lowering the loft, players would be wondering why their 7 iron now feels like an 8-iron... and the answer would be because its launching just like an 8-iron. I suggest manufacturers have lowered lofts so 7-irons still play like a 7-iron, just longer.
If you look at players clubs, I think you get a pretty clear look at just the pure technology changes. MP4 or MP5 buyers, for instance, tend to not care at all about distance (almost by definition, if distance was a major issue for them they wouldn't buy those irons). You see about 3* strengthened loft per club vs 30 years ago, but 8-irons still fly like 8-irons... just a little longer.