Why do Jawas have a "Demolitionmech" Droid

[kresty]

Smells like a continuity thing to me.  I imagine they probably didn't have names or purposes in ANH other than set dressing, so I guess the LIN class droids got a reason to exist later?  (Books or something?) 

But, given that Wookiepeedia's calling them "Demolitionmech" minelaying/mining droids, Savage and I were wondering what in the world the Jawa's could have been doing with one?  Or why they would possibly think the Lars would've been interested in buying one?

Not to mention which, Luke rubs his hand over one like when one admires a used car, why would Luke think an minelayer would be cool?  (Or even why would he think it would be wise to touch an explosives droid that had been in the "care" of the Jawas?)

I guess we know Jawas will salvage anything, so then the question would be why a mining bot used to set explosives would be used on a desert planet.  Blowing up a sand dune isn't gonna accomplish much!

Maybe some stupid off-world big game hunter thought it would be useful to take down a sarlacc?