The specification does have a hierarchical outline, and you can click on cross references too. Of course navigation can still be cumbersome, linking to chapters can also be awkward (tip: right click on outline element and copy link works in Firefox).

There are some problems of the spec though, and navigation is not the most pressing one. The spec is huge, support for less used parts is spotty in various PDF readers. It also has inaccuracies (not corrected in errata) and underspecified parts.