GWR often announce before Paddington departure that "the first stop is Westbury/Taunton/Exeter" (delete as appropriate) so anyone for Reading is taking a chance. Occasionally (very occasionally) they have missed out Reading if the train is already heaving leaving Paddington, not much anyone who chanced their luck for Reading can do but go to next stop and come back! They don't need to do it very often for word to get round the regulars. The threat is indeed enough to stop them trying.Regardless of any additional ticket purchase, the sheer journey time alone is simply not worth the risk. The announcements are clear enough, the next stop is not Reading!