but there's no way either one would be stupid enough to do something that makes them a pariah while the other doesn't.
That's the whole point of this. It is very likely that MS got wind of Sony considering the DRM stuff as well and that's why they went "okay let's go through with this." After the backlash though, according to sources, Sony has changed their mind.
What we're doing now is letting Sony know that we absolutely don't want drm, keeping this issue raised and in the spotlight, so it doesn't get forgotten or die down before e3, to prevent Sony from changing their mind back again (if this dies down too quickly, they will take it as "see it's just a kneejerk reaction, people will eventually not care and deal with it").
If Sony follows through with not implementing this stuff, there is a good chance that MS will be forced to not go through with their plans in order to remain competitive. This could either be done before the console even releases, could be done sometime after (depending on if there are 3rd party exclusive deals hinging on this feature, and whether microsoft wants to compensate them for not fully living up to the deal).
Of course, this isn't guaranteed to work, but we're giving it an effort. Sources have already said that MS even relaxed some of their policies in regards to the online requirement due to the reaction to the Adam Orth incident. Now the MS backlash after the event + this initiative could very well convince sony that going the route of no DRM for physical copies of games could be beneficial or an important differing feature.
If MS wants to prevent Sony from getting ahead though (which they have an opportunity to since their conference is first), they can announce that there is no DRM stuff, and that will take away the negative press, but it will also pretty much guarantee that Sony will announce the same thing.
Also the reason why it's directed at sony and not microsoft. MS in general has demonstrated a disconnect from the gaming crowd in the past few months. Sony's on the other hand don't. Sony is the first one to show any signs of changing their minds on this thing, whereas no news from the MS side.
So, most people are focusing on the company that's actually showing some sort of reaction to this issue and want to make sure that they keep on having that reaction. If some insider source info came out saying that MS is not considering DRM stuff anymore due to backlash, then people would be directing their tweets at MS as well.