PHP 5.3 as a requirement for a library?

I'm working on the Hamcrest matching library and have been considering the
switch to using namespaces (\Hamcrest\Type\IsInteger) instead of
class-names-as-namespaces (Hamcrest_Type_IsInteger). Coming from the Java
world I'm used to being forced to deploy my applications on versions one or
two behind the latest stable release. It was common to run on 1.2 when 1.4
was available and 1.3 when 1.5 was available for over a year. Managers are
fearful of new versions. Is this same pattern repeated in PHP?

My current company just switched to 5.3 after running 5.2 for some time. Are
we average in that regard or the exception to the rule?

Peace,
David