Sure, but that's true of almost every feature in a given DAW or application. If you don't want to use that DAW, you can't use that DAW's featureset either.
It's just another plugin, that people who are already using Logic can use (or not, they can still use third-party ones too). A lot of people using Logic aren't using third-party plugins at all, and I would argue that Logic doesn't to date actually have a good solution for saturation, other than overdriving the tape delay plugin, (Edit: As Mike points out, the PhatFX has distortion too - thanks) and as saturation has become an important part of a modern sound, having one in Logic is a good thing, imo.
We do this with third-party plugins anyway.
I don't really see it that way at all. it's just another tool you have available, for free, that someone can choose to use or not. I don't see any platform freedoms being restricted here, and nor is it anyway different to using, say, the ES2 or Sampler etc in Logic, which are only available in Logic, or any feature or internal plugin in Ableton Live, or anything else...
And there's always third-party options which work cross-DAW/platform, so if platform interoperability is important to a user, they will tend to leave the features that don't port alone (or render them into their audio files) and use third-party tools. Either way, the user has the choice. :shrugs: