The speakers on the M8 do not run the length of either grille; they're both a little less than half that long. If the renders you're thinking of actually are official HTC renders (and I really really really doubt that), then the grille on one side of the I-wanna-be-a-Samsung button could easily cover all of a speaker pot while the other could be either purely aesthetic or a cover for something like notification LEDs, microphones or (har-har) Moto-style motion sensors.