You're comparing the HMC80 MSRP to the street price of the HMC150. By the time the HMC80 hits the street, it'll be something in the range of a thousand dollars less than the street price of the HMC150.
With the exception of form factor and built in XLR inputs -- the answer to your question is exactly the same as any of the comparisons of the HMC40 with the HMC150.
EDIT: The HMC80 appears to have already hit the streets, and it's in the range of five hundred less than the HMC150. Give it a month or two -- the HMC80 will come down in price.
