Days after GOG publicly said cheerio to Codemasters' Grid, F1 2013, Dirt 3, and oh yes Grid have also disappeared from the Steam Store. If you already own them on there, there's no need to panic, as you'll still be able to download and play them, but if you were waiting to pick them up, then I'm afraid it's too late.
There's no reason given for the games' removal, and indeed no official recognition that they've gone at all, but if you try to search for all three games you'll find that they've been taken out to Steam's backyard and sho—er, sent to go live on a farm and no you can't go and visit them sorry kiddo.
GOG told us in an email that Grid's removal was due to expiring licenses, so it seems likely that the same explanation applies here. (Dirt 3 and F1 2013 weren't on GOG, so obviously they didn't need to be removed there.)