Saying "statistical area" doesn't give the whole picture because it doesn't tell you what
kind of statistical area. Detroit and Ann Arbor are only in the same
Combined Statistical Area, not the same Metropolitan Statistical Area.
Detroit—Warren—Dearborn, MI and Ann Arbor, MI are separate MSAs in the Detroit—Warren—Ann Arbor, MI CSA.
This means that while there are some interlocking commuting patterns between Detroit and Ann Arbor, they are much weaker than the commuting patterns within a single MSA.
On the contrary, Oakland is part of the same MSA as SF: San Francisco—Oakland—Hayward, CA. Though most of what was traditionally considered SV is in a separate MSA: San Jose—Sunnyvale—Santa Clara, CA. And both are part of the San Jose—San Francisco—Oakland, CA CSA.
Sorry, I'm something of a census nerd, and I even built a site using machine-parsed census data just so I could drill down to various levels.
Some links:
http://zaidan-x.org:8192/csa/220 (Detroit)
http://zaidan-x.org:8192/csa/488 (SF)