To add to the above post by tsz52 : the tau started with converted merchant ships and colonization craft as impromptu warships, then went through a huge fleet overhaul and produced purpose built warships, a huge improvement.
And the Tau
BFG play style is different to
IoM as is the Eldar, as is the necron, as is the chaos fleets, as is the Orks..etc etc.
The Tau are more of a ord. fleet with excellent torpedos, and attack craft and alot of them, just a different playstyle, not inferior (unless you cant wrap your brain around it ),
BFG was one of the few
GW games that actually acheived a very nice play balance, even though the eldar and necrons were always scary.
@ Asherian Command : the facts about the OB on taros is as follows, not the hyperbole you have stated :
Citing the Taros Campaign:
1 full company of Avenging sons Space marine chapter
2 full companies of the Raptors Space Marine chapter
10 full regiments of Imperial guard (3-4k troops per regiment )
and a scout titan detatchment.
Failed to defeat the Tau ( whom deployed around 100 hunter cadres aprox 8-9k firewarriors, and 5k kroot with 8k human aux )
So 3 Companies of the emperors Finest and 10 regiments of Guard around
40k imperial troops against a combined 22k of Tau and allies. and the Tau triumphed after a long campaign that was well fought and described in the book (Of course if all you want is see the
IoM win you can explain away the victory due to
IG incompentence, but oh well )
as per the stated one in IG3 Taro's Campaign.
and as many have stated already in this thread the Tau are aprox 1/3rd the speed of comparable
IoM warp speeds due to the current limitations to their technology, and a anology to their travel style is skipping a stone across a lake (the lake being the warp) they just don't delve far into the warp.
And as to the aformentioned war of dakka, yes the orks are winning, of course they are, its a fluff entry in their own codex, everyone kicks butt in their own codex entries

, same as the silly wipe out of a whole tyranid fleet with no losses by the Tau ( which I find stupid writing as well, but
GW has a problem keeping consistant power levels for all its factions.)