To me these sound too static, with too much of the same vibrato throughout. Even with a basic EXS string sound like String Ensemble, you could do better. Here's some suggestions.
Make the string parts less "in your face", it feels too up front and kind of distracting from the vibe you set up earlier.
Use long swells, subtle or otherwise, to create some emotion.
If you were using String Ensemble, notice that at lower velocities it has a less intense vibrato. Having different vibrato intensities can help with the "realism".
At the onset of notes, sometimes a small ramp in the volume can make it sounds less mechanical. Sometimes a long ramp up to a steady tone works.
Since the parts you've come up with are relatively simple, it would be a good idea to load up a variety of string sounds to try out. At least one could be a dedicated "low vibrato" preset. Another could be one that uses the mod wheel to control volume so you could easily build in swells. Experiment with different attacks, some fast, some slow. The mod wheel is your friend!
As Ashermusic just pointed out, there is a difference between "real" and "good". But in your situation, I think you could make your parts lean a bit more to the real side by following some of my suggestions.
BTW, for some reason, I can't get your song to play more than once, even if I reload your site.
Logic 9.1.5, MacPro quad core 2.8 GHz, 14 GB RAM, OSX 10.6.8, RME multiface