At both music stations I've been on which also stream on the web, this is what I've been told are the DMCA restrictions:
* No more than four songs by the same artist or group within any three-hour period, and the fourth must be separated by the first three by a song by a different artist or group.
* No more than three tracks from the same album or compilation within any three-hour period, and the third must be separated from the first two by a track from a different album or compilation.
I've never been told that playing two consecutive songs by the same artist or group is not permitted. I was told that no more than three consecutively is not permitted. If it was only two, then many commercial stations which also stream and play "three-fer" features would be in violation, such as WROR's morning "Beatle Break", which is three Beatles songs back-to-back. If I remember correctly, the WROR "Beatle Break" used to be four Beatles songs, but WROR cut it down to three, and I'm guessing they may have done that to comply with the DMCA after they began streaming.
Classic Rock WMLL "The Mill" 96.5 Manchester, NH does an evening "Box Set" three-fer artist feature as well, which also used to be more before they started streaming. WZLX plays more in their evening "Box Set" feature, but they can because they don't stream.
I do know of one streaming commercial outlying greater Boston area FM station which I hear frequently violate the DMCA.
Also, I wonder how WHRB at Harvard now gets away with doing their bi-annual "orgy" periods, devoting many hours, or even many days, to special programs devoted to certain artists or groups. I haven't checked, but I'm not aware of them shutting off their stream during their "orgy" periods.