One of the commenters on the article hit on a valid point, namely that an awful lot of people commuting south to Miami live out in the western Broward burbs and will never drive all the way east to hop on Tri-Rail; instead, they just drive down I-75, which is where there should be some rail. Interestingly enough, the FDOT has been holding public hearings this week on their project development and environment study for I-75. Initially, FDOT was going to consider the possibility of rail down the middle of I-75, but now they've scaled that back to special use lanes for express bus service. http://www.i-75vision.com/P_Info/P_Info.html
Ideally, there should be rail extending down I-75 and connecting with Metrorail, as well as east-west rail in both Miami-Dade and Broward (and rail running south from the western terminus of the east-west line in Dade). The penny sales tax increase for the grand Metrorail expansion was frittered away in Miami-Dade, though, and Broward seems to regularly shoot down east-west light rail, unfortunately.