Stats on Tumblr and WordPress.com show: Tumblr now hosts more blogs than WordPress.com does.
While the graph looks impressive the difference between the two is just 0.4%
The count doesn't include blogs using the blogging platform WordPress available from WordPress.org; only the hosted blogs at WordPress.com are taken into account.
Also, it's not known how many blogs on either site are abandoned.
Tumblr: More Blogs, Less Popular?
Search popularity for the two is hard(er) to determine. "Tumblr" can be a navigational or informational query. So can "wordpress" but that term can apply to self-hosted blogs as well.
There's virtually no search volume for "wordpress.com"
Given that the searches for "wordpress" must include destinations other than wordpress.com, Tumblr's search performance world-wide over the past 12 months is impressive.
Still, looking at traffic data as provided by Google Trends (and reflected in data from other providers), Tumblr has a lot of ground to cover before its blogs draw the same amount of daily unique visitors WordPress.com does.
Do you think the fact that Tumblr has more blogs but a lot less traffic means Tumblr just isn't that popular?