I don't care much for the rule either. I simply go by a rule in that I spread out double the normal cards before the end of the act. Therefore in a 4 hero game, I give them 10 shop cards to choose from. This way it keeps more surprise.
Sure, it keeps more surprise but...what happens if the item that your heroes want isnt in that 10? You said "oh...bad luck, now come to Act II and say goodbye to all Act I items..."
In this moment with the basic game + first 2 expansions, we have 33 Act I items...and with trolfens I dont know, maybe around 37
In a 4 heroes game, they should draw 20 Act I items before the Interlude, and of course they can draw multiple times the same item so...how many different items should they see before the interlude? I would say that maybe a 50%.
Its true that maybe, if the OL wants, they can play a rumor adventure and have the change of see 5 items more...but thats not sure.
Now, if you let them to see 10 items more after the Interlue, they would see a total of 30 items more or less...so there would be 7 items that they didnt see never for sure, and if the draw the same item more than 1 time...maybe they would lose around 10 items from Act I...
What happens if Rune Plate is one of that items? or crossbow? or the bearded axe? or maybe the mana weave, the chain mail, the ring of power...that items are BASIC for a good Act II and if you dont get them cause you dont have enought money, or you used it wrong ok...but if you dont have the chance cause you dont have "lucky"... it would be quite unfair especially when in the game there is a rule to avoid that to happens...
And think that in the future this would happen more and more...more Act I items, less % to get any of them...The chance to see all the items after the Interlude would be BASIC, now and even more in the future.