Responsive design is nice and is a very good and useful tool. If done right, it makes your site react better for a larger group of users.

However, your QA time and effort explodes when you do responsive layout. Your testing matrix goes from basically 2 operating systems and 4 browsers all at a fairly standard screen resolution target to supporting 4+ operating systems, 6+ browsers, and at the very least 4 significantly different resolutions/form factors as well as the ability for the user to change orientation.

Visual bug testing and layout issues add a ton of work and testing, especially at the beginning of a project.

Also, making a WHOLE site with multiple different areas, layouts, functionality responsive is a lot different than just making a single blog layout responsive.