Yes, they do send people traffic. Many sites rely on Google for most of their traffic. However, paid links does not a spam site make.
If they are flagging sites with a legitimate purpose and with original content, simply on the basis that their evermore dated method for determining authority is not working so well anymore, Google (as an authority themselves) should not be flagging them with such a label. I think it is unreasonable, not for denying them traffic, but for labeling them as spam. It's not impossible to find out who's in the supplemental index all of a sudden.
If they are flagging sites with a legitimate purpose and with original content, simply on the basis that their evermore dated method for determining authority is not working so well anymore, Google (as an authority themselves) should not be flagging them with such a label. I think it is unreasonable, not for denying them traffic, but for labeling them as spam. It's not impossible to find out who's in the supplemental index all of a sudden.