How is it harder to parse? Putting everything in separate lines make the CSS file 10 times longer, and it's more difficult to see groups of rules that fit together along with their common structure.
Nowadays unless you edit on a tablet your text editor probably handles 120 columns or more.
But I really can't see the argument for readability. When I navigate a stylesheet for a website I'm working on, I want to see the larger structure. I don't need to see clearly the properties within a single rule. I want to see from top down.
Still, this could be argued forever. Apples and bananas :) I guess it's the same discussion as space vs tabs, or 2 space vs 4 spaces.
Here's a better example from one project which used YUI2 (it's old, but I think it shows my point of view, that the dtk-skin-dlg structure is very obvious along with the hd/bd/ft structure YUI 2 uses and the styles applied to them, that's the structure I want to see readily when I work in a stylesheet without having to scroll to understand it's all connected together):
/* dialog body */
.dtk-skin-dlg .yui-panel { outline:none; }
.dtk-skin-dlg .yui-panel .hd { font:16px/1em Verdana, sans-serif; color:#ddd; padding:10px 10px 0; background:none; }
.dtk-skin-dlg .yui-panel .bd { padding:10px 10px 10px; background:none; font-size:12px; line-height:19px; color:#000; }
.dtk-skin-dlg .yui-panel .ft { padding:5px 10px 10px; background:none; font-size:12px; line-height:1.2em; color:#000; }
/* dialog footers, right aligned */
.dtk-skin-dlg .ft-right { clear:both; width:100%; padding:5px 0 0; text-align:right; }
/* left align buttons INSIDE ft-right */
.dtk-skin-dlg .ft-left { float:left; text-align:left; /*padding from ft-right*/ }
/* dialog body wrapper for extra css styling */
.dtk-skin-dlg .body { background:#fff; padding:10px; border-radius:3px; box-shadow:0 1px 3px rgba(0,0,0,0.2) inset; }
.dtk-mobl-dlg .body { background:#fff; padding:10px; }