If you look at the list above you'll notice that there are plenty of well-funded companies as well as bootstrapped companies. Zendesk has raised $85M. On the other end of the spectrum, you have Tender and Lighthouse from ENTP, which are not funded at all.

Unlike consumer internet startups, I think there's only one criterion for whether or not a SaaS product will be around in 5 years: Does the product work well?

Most of these companies don't/can't rely on network effects to grow, so there's very little winner-takes-all action. That's why you'll see plenty of breathing room for big players and small players alike in any given category.

Disclaimer: I'm the founder of a bootstrapped, profitable company, so I'm probably biased toward bootstrappers.

Revenue is the important metric. Funding can only delay the inevitable if they do not have revenue. Being funded does not mean you won't have to look for a new vendor in 6 months. Only the runway is a bit longer if the revenue isn't there.

I'd agree that this is one criterion, but being funded is neither necessary nor sufficient :)