I would assume that most people who frequent an internet forum already have an internet connection.
Anyways, I have used MLB.tv for probably 7 or 8 years now. I have never used Extra Innings. My TV provider didn't offer it when I first signed up for MLB.tv and after using the internet only version for several years I never felt the need to pay more to get it from a TV provider.The providers are in a better situation than they used to be now that they include MLB.tv with Extra Innings because the streaming version actually comes with more feeds and features.
The days of streaming video being lower quality than what you get from a TV provider are long gone as long as you have a fast enough internet connection. For many streaming services the video is offered at a higher bitrate than what you can get from a TV provider so there is less compression and the picture actually looks better.