It seems fairly reasonable that you could send a letter to Birmingham and have it delivered within two hours + travel time, but not to another part of the country unless you were lucky with the timings.
Remember, it was usually possible to post a letter from a station, which presumably gave it a very good chance of being on the next train.
[1] http://www.sutton-coldfield.net/rail/1902%20train%20timetabl...
If you were to then catch the 1000 train, arriving 1700, that would give the recipient time to get to Waverley in time for the arrival.
The letter got there first.
In 1840 average weekly wage for a skilled man in his 30s was £2 according to the first link on ddg. A penny post would be about 1/480th of a weekly wage. If we assume that a skilled man in his 30s today would earn £40k, that would put today's stamp in the £1.50 range, rather than 65p.
Far cheaper today, despite being pretty much meaningless. It's no wonder people "hacked" the system, this was a time before phones, or even telegrams, but a time when long distance commerce and connected economies were beginning to become established.
It's hard to believe. Whenever I mention this story to people and say it was all for the cost of a penny (the penny post being introduced in 1840), people say that back then a penny was worth so much more, we were able to invest in the infrastructure.
According to inflation calculators, 1p in 1840 is worth about 96p today. It's about 1/3rd more than a 1st class stamp today, and of course most postage is now paid for by bulk carriers (advertising), which is even cheaper.
There's some interesting stories to find in the economics of the UK postal system over the last 182 years...