Wordpress does the equivalent of the has_action when it checks the filter array for the presence of the filter.

I originally put the has_action in because one of the profiling tools I use relies on the 'all' hook to record wordpress flow and performance.  Having the condition stopped the flood of wpsc_meta requests from appearing in the profiling report.

I did observe that on my sites, where I have updated some of the checkout code and shipping modules to take advantage the customer meta, the customer meta profile calls are the most frequently used functions.  So the little bit of performance optimization may make a observable impact.  But there is no reason to be married to it if others feel strongly about removing it.