It's not about whether you can hear the difference between MP3 and Lossless. It's always blindingly obvious.
But you're assuming your use case applies to everyone, and that the reference is always being used for the fine details.
It never really should be for most mixing and especially recording contexts.
Once you get down to the fine detail, what's happening on reference track X has absolutely no real bearing on the track you're working on. You just end up chasing shadows if you chase that while you're recording. The differences in context between the two songs far, far out weigh the accuracy lost by using an MP3 as your comparison.
It's bigger picture calls that references are usually most useful for, at least in my experience, and for that an MP3 will always work. If the artist gives me a 128 mp3, then fine! 128 mp3 it is.
Similarly, if I'm using a temp track for overdubbing, why do I care about the fine details in quality? It doesn't make a blind bit of difference - again, the accuracy lost is outweighed by the fact the mix balance is going to change - so again, if it effects my recording judgement slightly it doesn't matter.
Would I request an MP3? No. But similar to the guy arguing back in 2012, I'm not going to push it back at a client either, unless it's actually being used in the output.