ZOB Controller voiced concern regarding unexpected routings resulting from clearances issued by DTW; noting more attention needs to be given to filed vs. cleared routings.

Narrative

Aircraft departed DTW; their route according to the flight plan; was DTW..DUNKS.J70.GEP..AXN. The requested flight plan was ..DUNKS.J70.ALPHE.J34.BAE.J70.GEP..AXN. The aircraft made an unexpected turn at ALPLE Intersection to the north on J34 rather than stay on J70. I asked the pilot if he was making a turn to J34 and he said yes so I told him to go direct PMM and join J70 to GEP. Recommendation; this has happened many times and could be dangerous as the planes make a north turn into traffic that they would normally be clear of. I think that Clearance Delivery at DTW fails to issue the right routing and just says 'as filed' to the pilot. The route part that is incorrect is in blue brackets on the URET flight plan in the departure proposal but disappears once the flight departs. The strange thing is the flight plan read out on the RADAR display still shows this route part where the URET does not; further leading to the confusion. I would suggest possibly informing the airlines to stop filing this routing to help things out; and also to stress to Clearance Delivery at DTW to make sure the routes are right.