well they ARE similar ( not the same but similar) , since they have 4x4 beat and rather similar drum structure/patterns
Of course to us sometimes the difference between different genres or between tracks of the same genre even, might seem huge, due to the different blend of all the layers and rhytms etc.
Remember that in the past there was no distinct difference between house,trance and techno. They started to get more seperate and distinct after 90s. (correct me if I am wrong).
And of course most electronic dance music is very repetitive music, but should we talk about REPEAT now ? =D