There is a cost to cleaning someones windows, insurance, petrol, equipment, ect. I know the cost per house on my round is more than £1, so that if I only charge a £1/house then at the end of the month I'd be in debt with out even attempting to pay any other household bills(income).
Sounds like the guy has income coming from else where as well. DHSS(lots do this), pension, spouse or another job, what ever the case he knows that his round isn't viable, it's just a beer money round, earn enough to have a few drinks that night.
If he's had the round for 20 years then thats 20 years of people not knowing what the true cost of window cleaning is and it's going to take you more than one visit to convince even just 50% of the round. At the same time your trying to pick up a new trade and be good at it. You say that your in a turning of town houses, in all honesty these aren't really worth doing for much less that £10. How would you feel if the window cleaner disappeared and a new one wanted to charge you a 1000% more, it's not really feasible.
There is also the chance that after selling the work he might reappear again, especially when some customers don't like the new price see him down the pub and ask him back. I'd canvass up your own new work at good prices, for every one of yours you'd have to do 10 of his.
Simon.