elementary's primary source of income is from pay-what-you-want downloadspay-what-you-want downloads. That accounts for something like 70% of monthly income. One-time PayPal payments and PatreonPayPal payments and Patreon account for most other income and we make a small amount on retail salesretail sales (shirts and stickers).
BountysourceBountysource is its own thing. When people contribute to our account on Bountysource, it stays in Bountysource. We never withdraw money from that account into our regular account. It is only used for bounties.
You're right that many people choose not to pay anything. The last time I checked, over 99% of downloaders don't pay.
elementary doesn't have any investors or outside corporate influence. We don't make advertising deals and we don't have any software products that aren't available at no cost. We only make money when our users give it voluntarily.
At the moment elementary employs just two people full-time.