Yes, you do
I'll answer the question-yes, you do sell on your website. (The only exceptions I can think of are pure personal expression or art sites.) Any commercial enterprise needs to sell on their website, as do non-profits like charities, NGOs and government agencies. (Although government agencies and other monopolies often don't need to sell products or services, they're wise to take a sales-style approach-few organisations are completely safe from disaffected citizens.)
A complicated offering demands more effort
"OK," I hear you say, "the web isn't all about e-commerce-but our clients would never make a decision based on the website alone." Although this statement is probably true, it's easy to draw the wrong conclusion-that complicated offerings require less sales effort online. In fact, the opposite is true. The more complicated your users' decision-making process, the more effort you need to put into selling on your website.
Research happens on the web
People increasingly do their initial research on the web-don't you? Typical research activities include finding potential suppliers, evaluating their offerings, screening, and short-listing promising candidates. Prospects will expect to be able to perform their research using your website-without calling you, and preferably without having to fight against the site's navigation or search. Additionally, the web's rise makes it easier to check organisations out-prospects might google for references, follow the links on your website, or look up staff on social networks.
The outcome of this research will strongly influence your prospects-often determining whether they contact you at all. And if they do call, their experiences when researching your organisation will have already created a strong impression of what you're like. You want that impression to be positive.
A paragraph probably isn't enough
The days when you could list your services, provide contact details, and then explain everything in person are over. Unless you're a near-monopoly, or your whole sector hasn't caught up with the Internet age, you're already losing out if you're not selling on your website.
It's challenging to convey an organisation's mastery of complex services, or the pertinence of its research techniques in a crowded field, for example. By comparison, e-commerce is easy-do you want this widget or not? Complex selling is more abstract, but it needs to be accessible, straightforward and persuasive-definitely worth spending some time on.