If your solid wood core sliding patio door is in close proximity to a pool, pond, fountain, stream, river, lake, waterfall or ocean... it will eventually rot. It doesn't matter whether your door has external cladding or not.
The deterioration and swelling of the wood core is most apparent at the bottom frame of the operating door(s) and/or stationary panel(s) and, although it can be apparent within 10 years, in most cases, it can take over 20 years for the softened wood to no longer support the rollers.
However, wood rot has been found to be severe in less than ten years with some Pella products and is not covered under their 10-year warranty. A class-action suit has attempted to address this consumer concern. http://www.youtube.com/watch?v=QH_G8cIvTb4
If caught in time, the deteriorating lower frame can be cost-effectively rebuilt.