The developers using open source solutions might be of the class "I'm using opensource solutions because they're better in this case," who Microsoft isn't targeting with this thing. They might be of the class "I'm using opensource solutions because there's no difference in quality, and the opensource stuff is cheaper." Microsoft is trying to make the decision harder for these people, but they're still not really the target audience.
This program is really meant for people of the class "I really want to use Microsoft products X, Y, and Z, but I can't, because I won't be able to afford licenses until my business has spun up. I'll make do with this opensource stuff instead." Now, I'm not entirely sure who these people are. Maybe they're developing desktop software or something. Provided they exist, though, this program could actually help them.
I'm one of those people and am happily using Microsoft products through BizSpark to develop web apps. Yes, I could use python with django or php with mysql (and have in the past); but I can build products better and faster with asp.net/c# (it's what I know and like best). And now that I don't have to pay huge licensing fees before I make a profit I can do that.
Personally, I use both MS and FOSS products extensively. I am a huge fan of Python and it is my primary scripting language, but my main career is as an MS SQL Server DBA, and I think that for many applications (not all) it compares quite favorably with mysql and oracle.
This program is really meant for people of the class "I really want to use Microsoft products X, Y, and Z, but I can't, because I won't be able to afford licenses until my business has spun up. I'll make do with this opensource stuff instead." Now, I'm not entirely sure who these people are. Maybe they're developing desktop software or something. Provided they exist, though, this program could actually help them.