Whats something asp.net does over php? I have yet to find something I can't do in php.
Not trying to get in to a "my language can beat up your language" discussion (I do like PHP and Ruby), but in my case its not a matter of whether or not I can do it things in PHP, but how simple/easy/quick it is to do so.
Its hard to beat validating records in my models (the M in my MVC app) by: validates_(insert some criteria)_of :attribute_name
or creating one-to-many relationships between models by: has_many :child_models
and belongs_to :parent_models
Notice the sysadmin-like lazyness. Now I finish a complete an app in a few days vs. weeks.
Not to say that someone couldn't write Rails in PHP, but there's a culture difference in Ruby that believes the *best* way to do things should be super easy, and everything else should be just easy.