Well, as a pixel artist myself, I don't build them for people to "use". I make them for the sense of achievement that comes when you place that last block of a big project, and the respect you gain from others as a skilled artist (In that area of minecraft pixel art). Yes it is nice to see people admiring your work for a short time; but even though it just might be a glance, they will still most probably take the time you spent creating it into account and credit you for it.
So basically, its all about the sense of achievement and the credit. Lol

But then on the other side of the subject, if you get "too good" at pixel arts and start making huge ones. People will start throwing around the hacker accusation. I had to deal with this myself and it was most inconvenient. The only way I resolved it was by entering in that tutorial contest a while back and submitting a tutorial on how I make my pixel arts. Unfortunately there are people out there who call themselves pixel "artists" when they just use importers or some other cheap way of getting credit for absolutely no effort. If it wasn't for these people tainting the reputation of the actual pixel artists who spend hours on their projects, pixel art making would be a whole lot more rewarding than it is now. But I stick to making pixel arts anyway because it is the only thing I am actually good at in minecraft and I see it as a hobby of sorts.

Well, I guess that's enough rambling for now. I hope you take my opinion into account. :3

The issue with in-game pixel art is that there's not really much you can do with it. If someone sees a nice piece of pixel art they can look at it, but that's about it. It's not really practical to put big pieces of art on servers as decoration, and you can't 'use' them like you can skins and texture packs. In that respect, in-game pixel art is at a disadvantage compared to other forms of decorative building.