IDM is a shit term that serves an important purpose. That era of guys were pushing the same boundaries and coming to different conclusions, and it's really hard to group them together without using IDM as a makeshift genre. It
does make sense to compare Autechre, Aphex Twin, and Squarepusher despite the fact that they ended up going in wildly different directions at times. Perfect sense. It would also make sense to throw Fennesz in there, someone who ended up even further away from any of them. And the only way to do it is underneath that awful phrase.
Portishead, Massive Attack, and Daft Punk aren't even remotely like each other.
I hate IDM label as well.
They're kind of sacred cow-ish, and I get the grouping. Daft Punk is super overrated (great, nostalgic, and Homework was dope as hell, but still overrated), Massive Attack is super overrated, and Portishead....well Portishead is just great, I dunno what the fuck Esch is on about that. Third is probably my favorite album of all time. How can a man love atmosphere in his records and not be in love with Third? You're basically trapped in a sonic-emotional minefield for an hour and a half.