A website is an online presence, and the majority of companies nowadays has some sort of online presence, whether it's just an advertisement in the online Yellow Pages or a fully-interactive e-commerce site.
Whilst people do still search for services in their local paper or phonebook, a lot of people will go to a search engine and what they need and the local area (e.g. landscaper in Henley-On-Thames), and instead of sifting through a phonebook or stumbling upon the perfect one by chance of advertisement, you'll be offered a whole list of landscapers in Henley-On-Thames and their websites. From here, people generally either go with the first result, or keep looking until they find what they're looking for. In which case, you need a website that stands out from the rest and does its job: pulling in customers.
In todays virtual world, if your competitors have websites and you don't, unfortunately, you miss out.