Is it so important?
Well it depends. Several major online business models heavily depend themselves by accessing certain parts of the web browsers cache which helps them to "evaluate". For instance, the Google Adsense uses these information a lot.
Say that you're coming from a web site which is about fashion related and entering a web site which is all about weight loss, then you'll see both "fashion" and "weight loss" ads in adsense ad blocks. So, from a user point of view, this is actually good thus making the user less "exposed" to others.
But from a marketing point of view, it is quite handy which is why Google haven't "introduced" it in the Chrome web browser (both Mozilla and Microsoft do offer this feature). So, even though currently Apple only controls about 6% of the current browser market... this is a pretty good move by them.
In the mean time, for Chrome users, there is an addon which disables adsense using their web browser's cache by using an addon called Keep my opt-outs... until Google decides to offer this feature in Chrome :).