Why downvotes? Maybe for many of you, the answer is obvious, but I think this can be an interesting question.
Certainly, some additional work goes into each separate version and you shouldn't just get that for free. But to pay full price for both versions seems wrong too. Might there be a base cost, with an additional cost for each system? That's as simple as giving Tam a discount for the mobile version after entering a legitimate license.
Just think about all the trouble: Mojang doesn’t use one payment processor, they use two and they would have to find some way to let customers prove to one payment processor that they used the other one.
That’s not all that problematic on their side (though still a lot of work), maybe they could find some sort of (semi-)automatic way to get a discount on the desktop version of Minecraft with a receipt or a code the Android app displays. (I would guess that at the volumes Minecraft sells something like this has to generate a lot of support requests, though.)
The much, much more common case (existing buyers of Minecraft for the desktop buy the mobile edition) is also much harder. I don’t think the Android Market has a built-in mechanism for entering codes to get discounts or something like that. (Maybe it has, I don’t know. I have never heard of something like that, though.) They would have to create a way for buyers to, I don’t know, maybe enter a code the Android app displays on their website to get a discount. That would again be work but at least it’s possible.
But how is Mojang going to get $2, $3 or something like that to the customers? Is there a way to easily do that? I don’t think so and even if the fees would be horrendous.
All of this is work and would also probably be a customer support nightmare.
It’s easier to just have one price point, especially if it is so low anyway. Hardly anyone will buy the mobile edition and not the desktop edition, how would it be worth it to create an additional price point for this tiny minority? It just doesn’t make any business sense.
The issue here is that this is not a port, it's a completely new mobile code base with a new internal developer behind it. It doesn't benefit directly from any of the work done on the Java version. It might make business sense to give some discounts to existing players, but I think the logistics of that would be difficult.
It's just not how the gaming business works and Mojang would lose money. It's a different game on a different system and probably required a huge effort to optimize code and trim it down to work on a mobile device. They could do a promotion at some point to give discounts but this will never be the norm.
Certainly, some additional work goes into each separate version and you shouldn't just get that for free. But to pay full price for both versions seems wrong too. Might there be a base cost, with an additional cost for each system? That's as simple as giving Tam a discount for the mobile version after entering a legitimate license.