There is a huge difference here. I absolutely hate VB
template system. Its an either or situation for most people. Vbulletin stores things in the database and while it might be easy for them to just apply diff patch's to templates since they are database stored it makes there database huge and slow on alot of systems and a bit more server intensive. I for one don't think you will see us switch to storing our templates in a database as it would not be the wisest thing to do but who knows what the future brings.
Our upgrade system is actually pretty easy if the instructions are followed. You can't compare VB
and Photopost as they are two separate apps. With Photopost you have file uploads as the main component and as a result there are certain permissions that need to be in place when doing things and when users have issues this is the most common cause.
We always look for ways to make things easier for customers just like the redesigned install script which I think is alot more intuitive than the old script. I think our one main problem is not enough documentation on install or upgrades and we need to stress highly certain things so look for improved documentation in the future.