The frontpage you see is the one that you compose yourself, that's the thing what makes reddit work.
So you end up with a tiny number of redditors who are the moderators for the largest sub-reddits. There is practically no turn over in these people, they have functionally complete autonomy over the vast majority of the traffic on the site, and they quite literally can choose to ban individual websites. What makes you think that companies were paying for digg power users to be friendly but the exact same class of users at reddit aren't getting the same treatment?
And in reality, what the majority of people see on the frontpage is the frontpage filled with the default sub-reddits. Which, again, are entirely at the discretion of handful of moderators who have 0 accountability.
This is a fair point. I'd argue that there is one single frontpage for reddit; each signed-in user has their own and this raises the cost of astroturfing with the same reach (%) as the universal Digg frontpage. Mods get their own fiefdoms in subreddits, but they don't wield the kind of power mr babyman had over the overall frontpage. This balkanization means disgruntled users are likely to leave subreddits, but stay on reddit itself, or if sufficiently motivated, create a competing subreddit (see the countless /r/X vs /r/true-X for any given X)