By the same logic, would that make Gary Neville England's greatest player?
It's not quite the same. Giles was the first big Irish star at a time when 'soccer' was first becoming a mass supported game in Ireland. He then became a leading pundit and by now is a sacred cow. He did win a great many honours with Leeds and was a good Irish manager.
Neville could hardly be described as a pioneering Englishman now could he? England had an illustrious history long before he came along and he's a Jonny-come-lately to the pundit's game!
Football is the third biggest game over here so to those who are considered 'football men' Giles was the first true star so he will always be considered one of the greats.
I think Townsend and Staunton should be much higher, there's a few strange choices but I guess it provokes debate.