Sorry for the noob question, but still I would like to clarify for yourself exactly why Mogento2 uses XML configurations, it is because of the protocol's REST?
This has nothing to do with RESTfulness or the like. I think Varien has chosen XML for its configuration to allow for a flexible therefore extensible, textual, standardized representation. Since you can override almost any configuration within your own modules, the main rationale behind using XML may have been the ability to easily add to, delete from, change and especially
MERGE nodes of the config DOM when combining the scattered configuration sources (which may be files or database entries).