A while back ago I would have agreed with you (also having spent a lot of time on Slashdot), but the quality of posts these days on the front pages keep from returning on a regular basis. Yes, I know that with Reddit you need to unsubscribe from the defaults and things like that and there are quality sub-reddits out there. But from my perspective, the front page used to contain enough good content that one could causally scan through and find something interesting without the haggle of signing up, maintaining subscriptions, searching for relevant content and things like that.
At the end of the day, I'm just there to browse and not jump through a bunch of hoops just to filter out junk that only appeals to the under 18 crowd.