There are some people that have just a crazy amount of retweets. I'm following Jeff Bullas blog. He has usually 100-500 tweets about his blogposts. I must say he provides excellent high quality (way better than what I'm writing here). Jeff has as of today 65'068 followers (and will probably have even more by the time this post goes out). He's blogging about Social Media:
Helping business and personal brands with digital marketing including social media with Blogs, Twitter, Facebook, LinkedIn, YouTube and Search Engine Optimization. Our goal "To optimize your brand in a digital world"
Clearly he writes FOR Twitterer/Facebooker and that kind. People who are actually using or thinking about using those platforms. I would therefor argue that it's easier to gain followers and retweets when writing about Social media topics, because you are writing to the people using it. Writing a blog about dogs or cats? I bet gaining followers and therefor retweets will not be as easy, and it's not that there aren't enough dog owners out there (proof: checkout some dog blogs)!
To cut a long story short: Depending on your topic it will be easier to gain twitter followers and tweets. If you are only about your amount of twitter followers, write about Social Media or be a celebrity.