I think "contamination" is a relative term.
If I was welding jet engine turbine blades, or parts for the space shuttle, I would be shooting for one level of quality.
If I was making a coffee table from 1" square tube, it would be a different story.
Yes, in the theoretical world, contamination of tig tungstens could be a problem. But for most real world applications, its not.
We run two tig welders pretty much all day every day. We mostly weld stainless, but with a fair amount of mild steel as well, some aluminum, and occasional copper and bronze alloys.
All the tungstens get sharpened on the belt/disc sander, both of which are running Alumina Zirconia, 50 grit CS411 from Klingspor.
We chuck up the tungsten in a makita cordless drill that sits next to the sander, and if the weldor is fussy, or the job precise, we use the belt sander, aligning the tungsten downward so the length of the tungsten is parallel to the direction of rotation.
If the weldor is quick and dirty, like me, since I am the boss, I just use the disc sander, and approximate a parallel grind.
I find it works just about as well, and since I have been tig welding for 25 years or so, I can fake it pretty good.
I used to use a grinding wheel on the bench grinder- and it was slower, not any better, and left big grooves in the grinding wheel- meaning periodic refacing of the wheel, fast consumption of the grinding wheel, and it was useless for anything else, as it wasnt flat. Cost more, too.
I find the disc/belt to be much faster, just as good a tip, and cheaper. The discs run me something like 3 or 4 bucks each, the belts a bit more, but they last weeks and weeks of use in a 3 man shop before changing.
We grind everything on this grinder- we touch up stainless parts all the time, sometimes even sand wood or plastic with it. Never had a problem with a bad weld due to tungsten contamination.
Of course, my welds arent getting x-rayed, but my guess is that for most average shop use, contamination, either of a grinding wheel or sandpaper, is just not a big worry.