Because fire warriors don't even get upgrades, and meanwhile guardsmen can be kitted out with lots of different roles. Tau usually assign things like specialized anti-tank and heavy infantry to the battlesuits.
Fair enough, and admittedly I COULD cheese out a bit by calling forth the Gu'sava or however they call it. Still, if there's plans for Vespids, Stealth Suits and so on I'd personally would wish for more variation in Tau setups. If only cause I'm derpish :S
My original plans WERE to wait out for the Space Marine and Chaos playertypes before I hosted it originally anyway, but I guess I can prep it out even still. Dang laziness and RL, y u making work so slow x,x
EDIT: Also, Tau weps have ammo, whereas the other 40k weps had ammo removed. This amuses me.