"Present Position Direct"

It happened to me for the first time in a long time on my last midnight shift. An aircraft departing a northeastbound runway on a westbound flight plan took off and called in. On initial contact, I said, "... cleared direct Sumspot VOR then on course, maintain FL280." The aircraft was expected to do a turn of about 120 degrees. After passing information on the flight to the next sector, I returned my gaze to the radar screen, seeing that he had made a turn and was tracking about 150 degrees off the runway heading. I let him go, watching him carefully, and confirming his equipment suffix indicated GPS on board. Eventually, I couldn't take it. The curiousity had gotten to me. I asked what his next waypoint was. He confirmed it was the Sumspot VOR. When I asked him about his track, and informed him of what the appropriate track would be, he told me he had made a turn to intercept the track between the VOR near his departure point and the Sumspot VOR, and his course would have had him intercept that track about 20NM west of the departure point's VOR.

I find this strange, personally. I'm not sure his interpretation is wrong, but it was unexpected. When I said, "direct Sumspot VOR," I expected he would go from where he was directly to the Sumspot VOR. Afterall, similar clearances are issued every day, and rarely have I seen it happen the above-described way in the 11 years I worked in the ACC. Some people around me have said they use the phrase "present position direct" to remove that interpretation and prevent what happened here. Personally, I see those words as wasted airtime, wasted syllables. Especially since the vast majority of pilots don't interpret my words the way that was described above. Am I off base? I understand that some GPS models will do this by default. Maybe that's not an appropriate method of operation for an aviation receiver? Comments?