It is somewhat infeasible to use linear colorspace, because you need a lot more precision in order to do this without banding. You end up with substantially bigger texture maps, possibly twice as big; but actually it ends up being a lot more than twice as big, more like 8x or 12x, because the compressed-texture formats that graphics chips are able to decompress onboard do not support this extra precision. So if you were to try using something like S3TC compression to reduce this bloat, the result would be really ugly.
In general, games only use light-linear texture maps when they also need HDR in the source texture, which is not that often. Ideally it is "purest" to use HDR for all source textures, but nobody does this because of the big impact on data size. (And even for the few textures that are stored as HDR source, often the data will not be integer, but some other slightly-more-complex encoding.)
[Claimer: I have been making 3D games professionally for 17 years, so this information is accurate.]
In general, games only use light-linear texture maps when they also need HDR in the source texture, which is not that often. Ideally it is "purest" to use HDR for all source textures, but nobody does this because of the big impact on data size. (And even for the few textures that are stored as HDR source, often the data will not be integer, but some other slightly-more-complex encoding.)
[Claimer: I have been making 3D games professionally for 17 years, so this information is accurate.]