Short anwswer: NO. A few sounds are similar, but they do not share the same waveforms and, even when they apparently do, they sound different (the Motif ES has a more "cold" sound, while the Tyros 2 sounds "warmer"; maybe this depends from the effect section, I don't know...)

Long answer: my opinion on the different sound categories is the following:
Acoustic piano: both good (depends on your taste)
Electric piano: better in the Motif ES
Organs: better in the Motif ES
Acoustic and electric bass: better in the Motif ES (much greater choice also)
Acoustic guitars: MUCH better in the Tyros 2
Electric guitars: better in the Tyros 2
Woodwinds: MUCH better in the Tyros 2 (the Motif ES saxophones sounds sterile and lifeless, by comparison)
Strings: better in the Tyros 2
Brass: better in the Tyros 2
Accordion: much better in the Tyros 2
Choirs and voices: better in the Motif ES
Pads: better in the Motif ES (more variety as well)
Synth sounds: MUCH better in the Motif ES (of course: it's a full-fledged synth! )
Drums: depends on what you are looking for; both have their strenghts and weaknesses.

So, to summarize, if you are after emulations of acoustic instruments, go for the Tyros 2, but if you are after electronic or synth sounds, go for the Motif ES...
OR, phrased in another way...
it depends on the musical genre you play most.

Hope this helps!