Though I'm not sure I agree with banning such clones, after all game mechanics can be neither copyrighted nor patented.
It's the art. Compare the screenshots of the various units to this:
While the visual similarities haven't causes Games Workshop to complain about infringement from Blizzard (as far as I know) it doesn't mean that Games Workshop isn't complaining about infringement in this or other cases.
However, it's telling that GW's notoriously trigger happy lawyers have left Blizzard alone, so it's pretty much a non-comparison.
From the look of the UI, it even has a time countdown slider for each turn, something fairly unique to Space Hulk. I kinda miss that, it really made Space Hulk tense. Still, it's a 20-year-old game, probably time for a remake somewhere :)