No offense Luke, but you need to stop making all these assumptions and guesses here. There is surely a solid basis behind why they did this which you seem to keep wanting to insist there isn't. They're a business and most certainly know more about this industry and their own specific situation than you or I do.
Just going off your unscientific survey of it's success, there would essentially have never been a game that has ever performed poorly from a sales standpoint. Even the most unsuccessful game that ever got any sort of retail release (We're not talking about things like Air Raid here) is going to have plenty of people online that own it, have mentioned it before, have reviewed it on Amazon if they stocked it, etc. In other words, your statement is all but useless when it comes to forming any sort of a guess on how the original performed at retail.
And they're not giving up $30 for each copy of the game for no reason at all. If the original did so well $60 like you seem to keep claiming despite no sales figures to support it, what's your rationale for them slashing the MSRP in half if all these people were lining up at their door to buy it at $60? What sort of idiots do you think they are? And what's your rationale for why they released it as a download if no one is going to buy it?
The evidence from the way this was released (Through a digital distribution channel for retail releases and untranslated) is that the original didn't do well or they'd of followed through with the sequel. Clearly, they think this distrbution method is the best way to go for this game and perhaps the only way if the numbers for the original just pointed towards there being no way to turn a profit. And perhaps the original did sell well from their point of view. But it's quite possible that the sales performance of the original wasn't impressive for the retailers. Nothing kills off a small niche release from a small publisher quicker than disinterest from retailers. They would need at least one or two big retailers willing to stock their game at release to bring it out. If they didn't, the game isn't happening.
Just use your head and think about this logically for a moment. If they thought there was any sort of a chance that this was going to sell well as a retail release at $60, then we'd have a retail release for $60. Since we didn't, clearly the performance of the original left them less than optimistic about the chances of the sequel. And since they're doing a download release, clearly, they think it has a chance.
They're not paying a very expensive ESRB review and fees to Microsoft if they believe no one is going to be buying this as a $30 download.