Rather than a technical discussion about whats new in PHP or getting into the holy wars over the best language ('PHP r0xors!', 'No, Ruby-on-rails kix PHP's ass', 'You NUBS just use Python'). Keep in mind that ultimately ZImbra wants to get the enterprise mindshare and its way, WAY, easier to get a big corporate enterprise to embrace Java than PHP, RoR, Python, et al. Ultimately if it were mostly PHP the big corporations would barely give it a passing glance.
Oh and by the way Ruby on Rails so kicks PHP's ass.