Serve HTML instead of XHTML
If there's one thing I don't like about some systems, it's their strict compliance to one standard or the other. Case in point is WordPress that locks you into using XHTML (unless you change it on the fly).
I was worried that CakePHP may have done the same but as it turns out, there's a handy file in /cake/config/ called tags.ini.php. Copy that file into /apps/config/ and edit the items in there to use the HTML syntax. Now your helpers should output using HTML instead of XHTML.