[kijin]

Sure, you can get part of the benefit even if you're on shared hosting. (Off-topic but related example: I use git to manage projects locally even if they are going to be deployed to a server that doesn't support git. Last week I finally moved a small-business client to a git-enabled host, and it was such a relief.) But it's only part of the benefit.

A good packaging system, for example, will track your PHP version and extensions and make appropriate adjustments. But what if your host uses a slightly different version of PHP with a slightly different list of extensions? At best, the packaging system makes adjustments again, and you cross your fingers hoping that nothing breaks. At worst, everything breaks because your host uses the wrong version of GD or whatever.

Every shared host that supports Ruby gets mired in requests for and complaints about specific versions of gems they've installed. I don't think it will be any different for PHP.

[wilmoore]

The problems you mention are why user land components should be used where possible and wrap builtins. Install the components local to the project and you control the outcome.