I'm not sure about the DJ apps, but I was specifically addressing Bushido's quote. If you read that quote, you're more likely to get that he was talking about a desktop browser interface for listening to music at work instead of a browser based interface for DJ'ing.
I did get the impression that he was referring to recreational listening at work, but ipedro's reply about DJing got me thinking.
Pacemaker indeed does let you access Spotify Premium to select songs, so one CAN use Spotify to DJ if one so chooses.