Does almost everyone from top tier colleges go to grad school?

STEM fields do vary in job prospects.

MIT has a career survey of earned PhD graduates. The 2014 report is at https://gecd.mit.edu/sites/default/files/about/files/2014-edd-survey.pdf . Pay levels:



Major           Post-doc                Other
                Pay     Number          Pay     Number
Math            62950   10              215000   2
CS              76429    7              137000   5
EE              50754   14              132569  27
Physics         60026   19              131667   3
Chemistry       53941    8              103200   5
Biology         42600   12               97750   4
Civil Eng       46500    4               96024   5
Chemical Eng    43000    2               93375  12
Bioengineering  41650    4               87500   2
Materials Eng   48179    7               86000   5