A problem about current sink

[refugee]

In the Allen's <<CMOS Analog Circuit Design 2nd Edition>>
When the author argued about that how the voltage divided by M2 and M1, He said that M1 should be Von+VT and M2 should be Von
But why? why can't the M2=Von+VT and M2=Von?

 

[A.Anand Srinivasan]

the author is talking about Vds i guess.... here M3 gate is at Vt+Von and it is so for M1 also... hence M1 has the same current through it as M3 and also the same Vds as M3 and hence it is at Vt+Von which is not the case for M2 which will have just its Von across it....