I believe the reason for this is because they don't want people to be confused by the difference between offering tokens and EOS network tokens, which are different things. Investors aren't buying any EOS network tokens because they can't. The EOS network does not exist yet.
Instead, investors are buying the Ethereum token that will represent the proportional share of the tokens they will issue when the EOS market is created.
I do not think that this means the EOS offering is totally legitimate, but I do not think that the disclaimer itself is cause for alarm.