I believe the reason for the surreal nature is to try to fool anti-spam software. Originally they'd have Viagra, then Vlagra and V!4gra and automatically generated typos Vaigra, Vagiar... But it seems that some anti-spam works on the basis of the ratio of recognised safe words to dodgy and/or unrecognised words. Obviously words like chainsaw and motherboard are "safe", so it can't be spam, can it?

That's the principle, anyway.