most of what's been said is true, but ignores the original purpose of wavetables. you CAN use them as just 'static harmonically rich waves', but that's not what they were designed for.
wavetables were originally done as a way to implement in the digital realm what could only be done in the analog world. remember, wavetables date back way before VAs, to the PPG wavecomputer 360. there were no digital filters etc. at the time. (and the wavecomputer 360 had no filter at all! the later PPG wave did have an analog filter).
the idea of wavetable synthesis is basic: you create a series of waves that implement a sort of 'harmonic series'. then you scan through it. for example, think of a filter sweep (to keep it simple, we'll assume no resonance). when the filter is almost closed, you just get a sine wave. as you open the filter, more harmonics appear, until it's wide open and all the harmonics are there.
ok, so what we do is we create a series of samples, one with the filter all the way closed (sine wave), the next with it a little bit open, the next a little more open, and so on up until we have a wave for all the way open. now, by scanning across the waves as oscillators, we can 'simulate' the filter sweep - instead of using a filter to shape the harmonic structure of the oscillator, we modify the oscillator to do the harmonic morphing directly.
but we aren't limited to filter sweeps, i can choose any harmonic structure for each wave... i could sweep between a sawtooth and a square for instance, or create a series of vocal formants and make it 'talk'. basically, by choosing your waves correctly, you can implement just about _any_ series of waveforms... you could possibly implement a flute blown at different breath strengths... a DX7 patch with varying modulation amount... etc. you only have a SINGLE axis to work with though in most wavetable synths, so you couldn't for example layout one axis for frequency, and another for resonance (though, with a 2D wavetable, such a thing is possible). wavetable though is about making the sound 'move' in the way you want it to, and not be limited to just the changes a filter makes.
the downside is that the wavetable gets 'quantized'; depending on how fast you are doing 'harmonic morphing', i.e. how different each sample is from the next, this might not even be audible, or it might be nasty. of course that's part of the charm of wavetable synthesis
the XT uses 61 waves in its wavetable; the ensoniq ASR samplers use 128 (afaik); with more waves in the wavetable, theoretically it can be a lot more smooth (as well as the ensoniqs are 16 bit); but the XT has a lot of other advantages of the ASRs. and you can do so much with filters, sometimes it takes a bit of imagination to 'go outside the box' - it's a bit like additive in that regard.
different from VAs? even VAs sound different. but a wavetable synth SHOULD be a lot more powerful, programming-wise, than a VA. which one you like better though is a matter of opinion.