Absolutely this.
It is, however, not the marketing strategy that failed them. G+ was hyped for some time before release and it became a hit since day one.
With the level of attention any Google product gained at that time, there was no need to focus on a niche. The issue were their horrendous decisions in UI and product design as well as feature integration. In short, it was a product for the tech savy user, yet aimed at the mainstream. It wasn't satisfying anyone.
I still can't understand why they would not cap the most valuable resource they had, GMail, GDocs, GCalendar, GReader, etc. Zero integration.