Chris Yeh presents his Grand Unified Theorem of Blogging:
The natural limit on the size of a blog’s audience depends on the degree to which the blog
1) sticks to a particular topic, and
2) creates a cult of personality around the writer.
Chris notes that we can’t read every post from every feed:
As a result, every blog reader will eventually find himself forced to winnow his feeds, to focus on those feeds that are richest in relevant content. The two basic measures we can expect him to apply are:
a) Does the post cover one of my preferred topics?
b) Is the post from someone I like and want to stay connected with?
The First Law of Blogging states that the more topics a blog covers, the lower the percentage of posts that will match up with the preferred topic set of any particular reader.
My blog is hardly "focused" — there are some themes, but it’s more general than most. This probably limits my readership (but it’s more fun for me). People, then, read my blog either because my eclectic set of interests happen to overlap with their eclectic set of interests, and/or because they’re interested in the author (me) and want to stay connected.
The maximum audience of a general blog like Ben’s depends on the extent to which he is able to build a Cult of Ben.
I would argue that "cult" blogs may have a smaller readership than a focused, rigorously topical blog, but the relationship between the author and readers is richer. In other words, because the ~2,000 people who read my blog regularly have decided to invest time in "Ben" (not simply in a sole topic like entrepreneurship), they feel like they know me, I feel like I know them, and it’s a more emotionally fulfilling exercise.
This being said, if your blog’s main purpose to make money from Google AdWords or be able to brag about having more than 10,000 RSS readers, by all means, the formula is clear: be focused, write a specialist blog.