If you want a user to have a role when the subscription is created create a workflow_ng event for that. If you want the role removed when the subscription is canceled or expires create a workflow_ng event for that. uc_roles isn't required. If a subscription is renewed it will add the amount of time to the expiration, regardless of when it happens. I'm not sure why that wouldn't be working.
I couldn't agree with you more, I don't understand why it's not always working. 
I tried to use the "Generic subscription" feature on its own on the product. I found that at times the role got applied, other times the order was processed and no role was given. Even better yet (and this one was a killer on the site for several months), we saw people who's orders were "Pending", or that were sent to Authnet and came back with a "Declined" credit card, and the user was given access!
We had a woman a couple of months ago who swore up and down that she should continue to have her access to the site because she paid for an annual subscription. Our records clearly show she *attempted* to subscribe, but the credit card number was invalid. The "Generic subscription" feature gave her the subscription role even though it was not supposed to do so.
I've just run into a bunch of situations like this where uc_subscriptions doesn't always work as intended. FYI, there also needs to be some type of rule in place that does not allow users to create another order if they are already a subscriber. I've done some things in Drupal to block access to subscription and order pages if someone is a paid subscriber, but this is problematic from what I'm about to write in the next post ...