Seeing as though every other club in the pro shop is a single club, i'm not sure why the iron sets consist of 8 clubs and all of them need to be the same set...
My idea is that, instead of a full iron set, They CAN be purchased as a full set OR separately as long irons, mid irons and scoring irons.
Confused yet? Here's an example (the one that inspired my suggestion): The Ping i15's long iron distances are unsurpassed, but, assuming that the i15's follow a similar distance formula to the G10's (i don't have this data cos nivlac's club compasion chart doesn't include the i15's), the G10 middle iron's hit just as far with a slower meter, and the Taylormade TP set hit's farther with the scoring irons and wedge. So, if a player wanted to hit as far as possible with every iron, he'd want the i15 long irons, G10 mid irons, and TP scoring irons (of course, the lower trajectory of the TP's complicates things but you get the idea).
So why not separate the irons into 3 groups? Considering the rest of the pro shop clubs are single clubs and not sets, i would think making an iron set available to buy in less than the full 8 club set would encourage players to try different models for their long irons and their scoring irons... or it could wreck the game :P. Who knows?