Precisely, you pay for one copy of the software at the current version. Upgrades are available, for free for a year. After that year there is a maintenance fee that covers both support and upgrades. This is a standard practice in the software industry, to my knowledge. One copy, software license, only allows use on one PC. Whether or not you choose to pay for the support/upgrade service is entirely your own decision.
If you only have one camera, the LE version will work fine. Given the level of technology and support that
Blue Iris provides, the cost of a licensed version is quite reasonable, in my opinion anyway. It would be nice if the license terms were further explained on the website though. You can always email support with any questions you may have prior to purchasing to get the most reliable answers.