I think the main problem is that you can't really get information about your enemy's teching in the early game, so you won't know that he tries lurkers, mass hydra, muta. Many players try to balance with preferring a 'universal-strategy' that is effective against all type of zerg units which i think don't exists so most protoss players must risk quite often and i think that is the reason for the dreadful statistics
early game units:
goon: goons can stop hydra and lurker (with cannon), but suck against massling or muta
archons: it is almost impossible to beat the toss with lings if he have archons, but they suck against mass hydra and with a good micro the zerg can keep muta harass in almost the same effectiveness, lurker is also good against archon
templars with storm: good against all type of unit especially ling and hydra, but mutas can avoid storm relatively easy, plus the stormed templars are really really expensive and they comu out sometimes too late
corsairs: buying corsair early is a perfect way to stop muta, but this is a totally different tech-way, so you can have problems by zerg ground units later
promote cannons: useless against hydras and they are way too expensive i think
i see the PvZ in this way, i am not so good player, so one can know better... it is just my opinion