Samsung already had their own RS version of their messaging app, but if the protocol gets fractured (as it's sure to be once US carriers start rolling it out - each one needs its own version for a few years, until the customer complaints overwhelm them [as happened hen each carrier had its own version of MMS, so you couldn't text a picture from one carrier to another]) Samsung will need a whole "RCS department" to keep up. Using Google's app just makes more sense financially - let Google spend the money.