I prefer and try not to include plugins with the theme because not everyone wants to use a specific plugin that I choose. I leave the plugins to the decision of the user, but I will make recommendations to select plugins. Also note that plugins that I use and recommend are not required for my themes which is important to not tie a theme to a particular plugin as it creates restrictions.
Regarding font sizes…I can and do plan on adding that, but it probably won’t be for “everything” in a theme.
As for the 100% sections and you mentioning the sliders, the difference here is that these are sliders and not “content” based elements such as you would have in a page or post. They often contain a lot of jQuery scripts to achieve those results. Long story short on this one is that sliders are very different from the content section method. It’s like using a fork to eat soup instead of a spoon. In some cases a fork works, but the spoon is better.