The Matthews funds are specialists in Asia; Oakmark concentrates on value. Such fund families are excellent at what they do, but it's unlikely that owning three of their funds gives you much more than you'd get with one.
Nevertheless, many of the big firms provide opportunities to diversify, and a handful, such as Fidelity and Vanguard, can truly claim to be one-stop shops. Moreover, many savvy fund families now offer their own fund supermarkets, which allow investors to sample funds from other shops while still remaining loyal to their favorite families. That's a win-win situation.