A 24-70 zoom meshes well with something that ends at 24mm, like a Tokina 12-24/4 or Sigma 12-24/4.5-5.6. I've hardly ever seen anyone who is content with having 24mm as their widest even on FF, but they buy a 16/17-35 lens which has a lot of overlap. So if you're going to have a dedicated wide anyways, a 24-70 makes perfect sense on APS-C as well, unless you need to shoot a lot around the 24mm mark and end up switching lenses all the time. Personally I don't understand the "24-70 doesn't cut on APS-C" notion... it just becomes a strictly standard zoom. After all, nobody blasts the 70-200 for not being something it is not, like a standard zoom to cover all bases. 
OTT, I liked the Tokina 12-24/4 when I had it, but others have reported that it is suffering from an inherent design problem that is going to cause malfunction sooner or later. I don't remember what it was though. Sigma 10-20/4-5.6 was also a decent lens (including usage on APS-H for fun), but probably rather slow by the standards of today's APS-C UWA zooms.
OTT, I liked the Tokina 12-24/4 when I had it, but others have reported that it is suffering from an inherent design problem that is going to cause malfunction sooner or later. I don't remember what it was though. Sigma 10-20/4-5.6 was also a decent lens (including usage on APS-H for fun), but probably rather slow by the standards of today's APS-C UWA zooms.