I'm not sure what you mean by spike-time waveform. If you mean the delta_G vs delta_t curve in your sample2.png, then yes, that's approximated by the example, though with a simplification for small delta_t. This shouldn't make a big difference unless you expect a significant proportion of your relative spike timings to fall between the two peaks.
Conversely, if you mean the action potential shape, then, welcome to the world of spiking models, where action potentials are modelled as instantaneous blips. You could, of course, model neurons with more physiological realism, but I'm not aware of any STDP models that avoid abstracting spike time to a single point in time anyway.