I think that effect is somewhat overrated. In the end, its best to let people get what they want. In that sense, not having information doesnt let people choose what they want.
Limiting what can be offered is more likely to prevent people from being able to get what they want.
Its possible that investors are very risk averse and so, are willing to pay a big premium for the preferred shares, one that employees are not willing to pay. In that case, employees actually win out on the deal, as they might not be as risk averse (as its only a small part of the compensation).
But in that game, the employee is barred from buying unlimitedly (min 1mm in assets) and also from knowing what everyone else is getting (which investors know).
I cant emphasize how big a loss it is to not let employees invest. Employees know a lot of things investors don't and share that information amongst each other, but can't give market signals because they cant buy or sell or disclose freely. I.E. if you saw a company where employees are all buying shares now, its great for both employees and the general public AND investing in general.
Not only that, but not being able to sell and exchange shares between employees means you cant hedge bets as employee. For example, you could pool a bunch of startup shares that way. Thats only for investor groups today.
Sometimes when I think the US is supposed to be the pinnacle of economic liberalism, I shed a few tears.