I'm going to try to answer this question, even though I would like to know myself what numbers the question is based on. Has their been data pulled and put in a post that suggests that most steemians doon't upvote? Or don't upvote enough?

Upvoting vs RCs

In the many situations where lack of RCs stymies any type of consistent activity, RCs can be an issue regarding voting. However, since the emphasis is on what is considered 'excess' RCs, or what I'll just call enough RCs to function normally, RCs aren't really the main consideration anyway.

Voting Power

What probably does come into play for most users with enough RCs is their voting power. Regardless of the size of the account, each user can only make 10-11 upvotes with 100% voting power within a 24 hour period. Most people don't upvote that way, but do so in smaller percentage amounts, some with the intent of getting a post or comment comfortably over the dust vote threshold. That means upvotes of at least $0.02, though higher is better due to reward allocation degradation.

So, if people aren't upvoting, voting power might be an issue.

VALUE

Another reason why users might not be upvoting is because of not finding enough posts or comments that they find of value. Most people will refer to this as not finding quality posts, even though quality is highly subjective. So is value, but in my mind, it allows for some people finding value in something while others don't, while quality could be considered to meet certain agreed upon standards (except on STEEM, where it's hard to get a consensus on much of anything).

VISIBILITY

It's tough to be seen. Even with lower posting rates, there's still plenty out there to see. Things can get lost really quickly if people aren't specifically looking for them. Most people follow an insane amount of other users, making their feeds impossible to curate from. They might have GINAbot to alert them when a favorite author upvotes, but doing so limits them to whoever's in their notifications.

AUTOVOTING

A lot of people upvote, but they don't really curate. What I mean by that is, they don't actually read the posts they're upvoting, but rather, some curation trail is doing it, or they have read a few posts by various authors, decided they're worthy of an upvote, and then lock in the percentage for that user. In so doing, if they're checking periodically, they might discard some who are no longer meeting value expectations, go search for someone else to the list, or they might just let it run indefinitely. In such a case, they end up just upvoting those they initially found.

So, in reality, upvoting based on sufficient RCs to do so isn't really an issue. It's based on things I've mentioned, any combination thereof, and probably some other things I've missed. I can't see anyone trying to horde RCs by avoiding upvoting, however.