Fiiiiiiiiinally!! 
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Yup, delays included:
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Thanks.
During my testing, I noticed alerts for service changes and holiday service, so it does seem that Apple provides appropriate notices if necessary — not sure about delays or cancellations in particular though.
In terms of data sources for transit info in the UK, Apple has yet to update its acknowledgments page beyond London, where data is apparently provided by "ITO World Ltd." See: http://gspe21.ls.apple.com/html/attribution-44.html
Yup, delays included: