Currently, there is a mix-up of capitalization in the messages regarding terms that represent software concepts. The affected terms are, for example, "s/Statement", "i/Item" and "p/Property" while, for example, "qualifier" and "label" are only present in lower-case at the moment.
In terms of consistency, there should be a policy on whether to apply capitalization to terms that inherit software concepts. Personally, I would propose to always capitalize such terms as that would stress their special meaning. "A statement" is not the same as "a (Wikibase) Statement"; See also: http://en.wikipedia.org/wiki/Proper_noun, and, in particular, http://en.wikipedia.org/wiki/Proper_noun#Capitalized_common_nouns_derived_from_proper_nouns