One is audience. At my Alberta lecture I got a large turnout from the broad CS department. In regular colloquiums I usually just get the CS Theory types and people I know, though at Penn State I happen to know faculty ranging from pure logicians to experimental economists.
I'm more likely to accept an invite as a distinguished lecturer. I don't usually travel to give a regular seminar talk unless I'm using it as an excuse to visit specific people and I didn't really know anyone at Alberta well save for one former NEC colleague.
Perhaps the biggest difference is attitude. As a distinguished lecturer, people want to talk to me, my schedule is booked solid shuffling from office to office much like an interview trip. People want to hear what I have to say because I was "distinguished". I have no shortage of opinions and I always like an audience willing to hear them.