Using WordPress can help a lot of people to get onto the website building bandwagon quickly and easily. However, how much time and cost you want to spend on making it up and running? The contingencies for using WordPress are:
- You are tied to the hosting site
- You may be trapped by the support expense
- You spend more time on learning new skills which may not be a must-have
- You cannot access configuration files php.ini, httpd.conf
- You can only access the database via control panel
- You may face additional security issues and cross-site contamination issues 
- You lose the control when you need to upgrade to build more dynamic content
There are lots of videos about how to make a website in a few hours. They are for business users and meanwhile create the job for the affiliates. It's similar to the SEO market campaign for business. While businesses feel like they can save money on the PPC (Pay-Per-Click) ads, they actually spend more money on hiring SEO marketers to fine tune the keyword combination for them and keep tracking the result, day in and day out.
The primary answer is every startup company has its big vision/mission and aim to be big. However, we have to start small and focus on the niche market, as I was told many times.
If you don't have enough time to apply the HTML5/CSS3 in your website completely, at least a vanilla WordPress development environment and production deployment environment can help you to keep the control in your hands. And you can handle all the security and version control issues by your self. Don't you agree?