That's a basic rule that can be applied to lots of things: If a company offers a lot of different products or one product that can do everything, usually none of those are really good. Typical example would be a restaurant that serves everything from pizza/pasta, asian cuisine/sushi to steak, burgers and so on
@Sina@Blaubarschmann Google is more like a restaurant that has a large chalk board covered with specials. The kind that has a soup of the day, and a fish of the day, and a chef's special.
There are a few core menu items that are perennials on its printed menu. Search, maps, photos, ads, Gmail, Google Docs, Chrome, Android, Chromebook, YouTube...
Then there's the messaging app of the day, the TV platform of the day, the flavour-of-the-month device selection...