I’ve been writing this for nearly 10 years, and in that time a lot of things in online marketing have had their day. Unfortunately, we probably all work with people who heard about something once but didn’t get the message that it went away. One of those things is ‘Exact Match Domains’. There was a time when you could put up any old flimsy bit of content on its own website, and as long as the search term was also in the domain name, you’d get a decent rank in the Google results.
As you’d expect, once the market became flooded with poor, one-page sites designed to spam the index, Google just amended its big black box to treat these sites with the contempt they deserve. That was five years ago.
Some sites built around a search term continued to do well however, and this made it difficult to convince people that just having the term in the domain name wasn’t what was doing the trick. The reason the sites did well turned out to be that they had a decent amount of genuinely useful content, and probably links from other sites too. The keywords-in-the-domain-name thing didn’t hurt the Google ranking, but it didn’t add much either.
I’d still argue that it’s best for SEO and business in general to keep all your company’s assets on one domain. As an analogy, suppose a big high street store wants to enter the blue widgets market. What should it do? Open up a blue widgets department inside the store, or set up a separate, small shop down the road? To me the answer is obvious, whether or not the store is already known for being a destination for other parts of the widget market. The only real advantage to having a separate store is to act as a billboard to say “we now sell blue widgets”. But if that’s the case, why not buy a billboard? It’s probably cheaper. By having the blue widgets department inside the existing store, you get to sell to the shoppers who already know you.