So I went through technical support because I had this exactly some problem. Smart playlist shows up in iTunes on my iMAC, as well as via Apple TV (both via iCloud and Home Sharing options.) It also fully populates those smart playlists.
For my pre-existing Smart Playlists (that only have criteria for the GROUPING field) show up, have songs, but are quite a few songs short. I then created a brand new play list with brand new tracks... and its empty on iPhone 4S and iPAD2. Apple TV and IMAC are fine.
So technical support provided me with this response: For smart playlists to work on iOS devices, the songs must be downloaded to the device.
My feedback was this: So this is chicken and the egg. You create the playlist to easily locate and download those songs to your device, but you cant because they have to be on your device before they will show in the playlist.
I suppose the only work around is to create the smart playlist w/ your filters. THEN create a regular playlist and copy everything in the SMART Playlist into the regular playlist.
I have not used Apple products for very long... approaching 2 years. I moved everything to Apple. Computers, laptops, portable devices, etc... I have been VERY impressed. HOWEVER, this makes the point of Smart Playlists completely manual when it comes to your iOS device.
I will for sure be launching a compliant to www.apple.com/feedback.