Quite.
One does apply some common sense every time one travels. Stick to the advertised connections and you're usually fine. Given that many times I end up connecting two or three times en route (say, Oxford to west Wales) with most of the services involved running roughly hourly, I could allow myself an extra hour for each connection and double the length of the journey it's true. Why on earth I'd want to though I have no idea.
I can only go by personal experience where I have made many hundreds of journeys involving connecting trains en route - nearly always there has not been an issue; occasionally there has but the time that such delays have cost me pales into insignificance compared to the time I would have wasted messing about to ensure that I had half an hour between connecting trains!
no doubt if you miss the 1844 off Swindon there's another train an hour later.
Erm, putting things politely, that's something of a bone of contention for the resident of Melksham. There isn't another train until the following morning. In fact the poor service provided en route was one of hte original raisons d'etre of this forum!