Never judge a theme just by its demo.
Always have a look at a theme’s documentation and layout templates before making a decision.
internet-weblog theme uses a
micropost post type that displays the full body of a post on the homepage unless its link points to an external URL.
Also by default if a post uses the
No. If true, Microposts will be summarized in the main list just like posts with a continue reading link. If not present or false, the default of not summarizing microposts is applied.
The relevant code about homepage post previews of the
theme-ink theme can be found here
As per the linked template, different things happen whether a post has a title, a description and if its content is above 120 characters, however IF a post does not have a title then its content is displayed in full on the homepage.