The key difference between a branded house and a house of brands is, ultimately, which brand reigns supreme. With a branded house, you deal with a single brand (Google), and every product (Gmail, Calendar, Search) layers up to the primary brand. On the other hand, with a house of brands, each product is independent of the next. So, for example, Gillett, Bounty, Pantene, and Oral-B all have unique brands which lead, even though they’re owned by Procter & Gamble.
Typically, a house of brands has unique audiences, branding, and sales strategies. And many of the major CPG companies all have to support unique brands.