@Konstantin -

TT is a little bit weird. I mean who builds themes with a file called loop.php?

It may be unconventional, but I do something similar. I have a "post.php" file that essentially just contains the loop. I use a (minimal) few conditionals to modify the loop for single, page, archive, and home, but otherwise, it's 95% the same code for all three.

Thus, I can more easily change the layout for the different template file types (primarily, index, single, page, archive) while more easily and consistently managing the loop.

It may not work for everyone, but it works for me. :)