Not at all.
After all, a blog
is a website.

Blog software is simply a type of web content management system.
There are plenty of people who only have blogs, not traditional websites at all. A few professional bloggers actually make their living writing blogs. There is no requirement at all that you must have a "traditional" online store or brochure-ware website in order to start a blog.
The only requirement for you to start a blog is that you have something to say.
That said, blogging requires time and effort. And before you commit yourself to the ongoing task of blogging, it's probably a good idea to realistically evaluate your chances of getting out of it what you think you'll get out of it.
So... here are a few questions to jump start the evaluation process.

What do you anticipate the results of your blogging to be? Trying to be as objective as you can, what do you think your realistic chances are of attaining those results? Are your potential customers online in the first place? What will you do if the blog doesn't achieve the desired results, or if it takes longer to "catch on" than you expected? How much time and energy do you have to invest in writing posts (or how much money to pay somebody else to do it for you)? How much time and energy do you have to invest in promoting your blog (by reading/commenting on related blogs, guest posting on other blogs, etc.)? Are you mentally prepared for the "long haul"? Can you think of enough interesting things to write (not just sales pitches, but interesting article type stuff) to keep people coming back?
Good luck and happy blogging!
--Torka