They are sized so the people running them on Android on their phones can get them done in a reasonable time.
Cheers

I do not mean to be presumptuous of how the techs are sizing tasks, but I think they are attempting to find a balance of not making the tasks too short for the PC's and too long for the Android phones. If they are too short, the number of WU's done tends to overwhelm the system and if they are too long they will frustrate the phone users. All of the systems are evidently pulling from the same pool of WU's with differentiation only for the platform. This one of the items which is under consideration for the future where faster systems will get larger jobs and less robust systems will get shorter WU's. Perhaps Sekerob or one of the techs will chime in with additional information.
Cheers

I have recently installed Boinc with WCG but still after 4 days am unable to receive any tasks, could this be due to insufficient cpu power on the phone ? thanks