You are spot on. I think they did it to make them look a little different then there new Mars 2 series even though they have the option of veg and bloom.
Well, we know it's not for "safety" reasons as I'm sure Tina said they were considering removing the plastic cover, but my own personal view is that unless it's there to conform to IP ratings then it shouldn't be there.
Would have been nice to know what even "lux" levels were before and after removing the cover, just because I get curious about these things.