What is the difference? All they are doing is giving you a different way of accessing them. It's the same bloody company! It's not like they've created and passed the photos on to someone else, they're just in a bucket with "picasa" written on it.
Google needs to make it much clearer that signing up to a Google account gives you access to all Google services. Their current sign-up page shows a line of tiny Google icons which completely fails to convey this. The icons are one image in a row, so you can't even hover over each icon to see a tooltip description of what they are. Once again, this is just clumsy UX.
In my view, if a user signs up for a particular service such as Gmail, only that service should be activated. Other Google services are only activated when you actually decide to use them (i.e. don't create an empty Google+ site for me unless I opt-in to using that service).
Perhaps this comes from different expectations. When I signed up with google this is exactly what I expected, to have access to every service they offered at that time and all future services.
> (i.e. don't create an empty Google+ site for me unless I opt-in to using that service).
This one I can see more (although I'm not sure quite what happens here, I'd need to create a new account and have a look).