There are other fees..... from ICANN depending on TLDs you are selling to your end users.. not to mention bandwidth, servers, API implementation, front-end coding, WHOIS service etcetc....
Direct pricing for consumer market is always higher that pricing for resellers.... ENOM has good strategy for resellers point of view.. selling at low price to resellers and high-prices for non-resellers....
BUT this is the point. There are many users who do not know that you can get domains for <10$ per year. There are still many that buy from register.com and verisign.com and other domain registrars that charge $70 per two years....
Always remember, that it's harder to find a client who pays 35$ per year, but then again, if you are selling domains for $10, you should sell higher volume to make the same profit...