He is right in that its direct injection that causes the build up and that its caused by oil vapour being recirculated back into the engine via the intake manifold.
On non DI cars this happens as well, but as fuel is injected through the intake manifold it has a cleaning effect and the build up never gets the chance to happen.
AFAIK there isn't a way to clean it other than manually strip it apart. Although unsightly, I doubt its going to give anyone any concern for a long long time. The technology has been used by Audi for quite some time with no significant issues.
A catch can would be the most effective way to stop it happening.
