I read this to mean that points can be purchased in conjunction with any type of redemption, not only a transfer, but it is true that you cannot buy them just to have them sit in the account.
I read the Amex Membership Rewards Terms and Conditions the same way. However, when I tried to buy 500,000 points and immediately redeem them into my British Air Account it was refused. I spoke with several MR representatives and at least one MR Supervisor who told me their "system" would not let them do this as my MR account already had a balance of over 500,000 miles. I even spoke with one Rep who agreed with me about the wording of the Terms and Conditions and had been able to do it in the past, but said "they must have changed the computer" because "it won't allow me to do it".