Services module and hook_node_view
hook_node_view() is only invoked when a node is prepared for display (normally either through node_view() or node_view_multiple()).

Since the node isn't prepared for display when you request it via a services call, your hook won't be called. If you think about it this makes perfect sense; you're requesting a json/xml representation of the node so there's absolutely no reason why the node should be prepared for display.

The only way round this would be to move your logic into hook_node_load(), which is called for all node loads. The same data that you attach in hook_node_load() is available to you on the node object in hook_node_view(), so you'll be able to move your logic without any problem at all.

I suppose the other, more complicated method, would be to write your own Services resource that loads the node view as well as the node, so the extra data you're adding would get picked up. 

But semantically speaking, unless the actions you're taking relate specifically to the HTML that will be output for the node, hook_node_view() is not the right place to add your extra data.