You mean the standard OS X shortcuts if you use a US keyboard, right? The shortcuts on a German keyboard (which does not have [ and ] keys) for back and forward are Shift-Cmd-Ö and Shif-Cmd-Ä (that’s using Safari), clearly inferior to Cmd-Left and Cmd-Right.

Cmd-Left and Cmd-Right are necessary.

(Google Chrome has actually Cmd-[ and Cmd-] as back and forward even with my German keyboard layout – which is quite dumb and shows that they don’t seem to care much for localization. Cmd-[ translates to Alt-Cmd-5 on a German keyboard.)