First, this is about Game Design and not programming. Programmers generally don't get a say in game design.
Secondly, this isn't about reducing attack speed in total, it's about reducing the attack speed bonus on items; it was a very over-powered stat and made other stats almost unchoosable by comparison. Not that you'd know, because apparently, you don't play it.
Thirdly, the game isn't uncompletable by a small percentage of the gamer population. There's really quite a large amount of people who beat it at Inferno, but for a casual gamer, playing at Normal, Nightmare and Hell could be just fine (and get to level 60, the hard level cap). You don't miss out on any of the story and the final difficulty is for the gamer who wants more. If you didn't know, to get to Inferno, you'd have to play through the whole campaign 3 times, so you don't miss a whole lot.
Fourthly, somehow Blizzard being a reputable company makes me sticking up for their decisions "unfounded." So, if they were not reputable, I might have a better stance? I'm not quite sure if you know how this works...
Look, Blizzard has quite a reputation with releasing fixes that nerf builds left and right. If you didn't know, balancing an multiplayer RPG is quite a difficult task. The more expanded it becomes, the options you have to consider grow exponentially and you simply can't keep track of all. Hence fixes and nerfs after release. The gamers will find which work and which disproportionally work and stats need to be fixed in order to balance the choices.
Fifthly, somehow you made the connection between defending a game design choice from one of the most prestigious studios around (and mind you, I can go further into why the choice to nerf item attack speed bonuses is a good one) between defending some of the categorically worst games out there.
Maybe game design is a mysterious concept to you, but it's good game design practices, like balancing out build choices, that separate good games like D3 from the poor ones. Yes, some gamers will be butthurt that their build depending on an overpowered option will become less powerful, but that's an inevitability. They'll rant on about it, but they'll still sink another 100 hours in D3, and not other games.
You know, if you don't know about something, it's okay to just admit it. We don't have to take the long way around and have me show you why you're wrong.