Thanks for the reply.
I would say PT is the geographic region that switches between PST and PDT, while PDT is a specific offset from UTC.
In fact, Wolfram|Alpha displays a widget in the results denoting the time offset from GMT, which is equivalently the winter timezone for the UK. GMT is not currently in effect there either (currently we're under BST), so I'm not sure your interpretation would be consistent with that aspect.
As I interpret it, regardless of whether they are geographical, PDT being defined relative to GMT means it should always be GMT-7. Even if we disagree about whether we should even bother calculating in PDT throughout the year, I would expect Wolfram|Alpha to display an exception rather than something confusing and/or wrong.
