OK, but note that I said "with the same specs".
If you take, say, a "Standard Power (77W max TDP)" and "Low Power" (65W TDP) Ivy Bridge part at the same clock speed, the performance will be pretty much identical. It's just the Low Power parts cost a bit more.
A "mobile" Ivy Bridge part really just means it's Dual Core instead of Quad, which more-or-less halves the TDP. A desktop dual-core Ivy Bridge is the same, performance and TDP wise, as a Mobile part - just packaged differently.
And I'm pretty sure all Ivy Bridge parts support things like SSE4 - even the Ultra-low-power versions.