I'm not sure who voted you up, but the second part of this comment looks trollish (apologies if it wasn't).
For a starter, this is a very small subset of computer science conferences (e.g., the main software engineering and programming language conferences are missing). I'm not sure in which field Yahoo! Research works (looks like data mining), but in SE and PL, they are inexistent.
Best paper awards are just one metric among many. Citations, venue impact factor, number of publications are other (imperfect) metrics. It's probably fair to say that MIT and other big universities and corporate labs (IBM and Microsoft) have high scores in all of these metrics, whereas Yahoo! Research is still too young and too small to compete with even smaller but dynamic universities w.r.t. these metrics.
For a starter, this is a very small subset of computer science conferences (e.g., the main software engineering and programming language conferences are missing). I'm not sure in which field Yahoo! Research works (looks like data mining), but in SE and PL, they are inexistent.
Best paper awards are just one metric among many. Citations, venue impact factor, number of publications are other (imperfect) metrics. It's probably fair to say that MIT and other big universities and corporate labs (IBM and Microsoft) have high scores in all of these metrics, whereas Yahoo! Research is still too young and too small to compete with even smaller but dynamic universities w.r.t. these metrics.