Removing the underline from a:link and a:visited in the default theme was an aesthetic change which carries significant rammifications in content interpretation.
For as long as it has existed, E2 has had this weird thing going on of lots of underlined words scattered throughout sentences. (As an aesthetic quirk of online writing, blogging has finally pushed this convention more into the mainstream. One alternative, which E2 has always implicitly frowned on, has been to link in a parenthetical at the end of a sentence (link).)
This underlining emparts added emphasis to particular words. In general, E2 authors have accepted the mandatory thou shalt hardlink directive because they have to, and have worked the aesthetic into their writeups in a variety of ways. Consider a few:
By removing the text decoration from a:link and a:visited in the default theme, the emphasis placed on links has been removed by default. In many extant writings, the emphasis was an integral part of the piece. Whether or not the emphasis on linking itself is as well lessened is not my concern, although I expect it is a concern of others. However, if new noders are to be expected to node for the same ages as others, they should read the old nodes with the emphasis that was intended. Afterwards, they can pick a theme without text decoration.