knowmiddlename
You can look at it from a PC prospective. A graphics card processor performs a narrow set of highly repetitive pixel parameter calculations required to show changing images on screen. Due to specialized design and instructions set it works very fast, unloading the main processor to coup with other various tasks, which are not so repetitive. An STB is also PC like, it has main processor, memory, peripheral devices like tuners, requiring drivers to work under that STB's OS.
Similar to a Graphics Card chip, sat tuner and demodulator chipsets do their job with TV channel data that is coming from the sky, which is really just endless sequence of digits. Newer demods have higher feature integration, and usually incorporate blindscan circuitry. They are controlled by an integrated into the demod microprocessor, so work fast. But blindscan will work only if its instructions are supported in the tuner driver and current STB firmware, including its interface that a user sees on screen. Older demods didn't have blindscan circuitry integrated, so it was added on PCBs of some receivers, and still require firmware support. If there is no dedicated circuitry, then a firmware developer can try instructing the main proc to do the blindscan job among other tasks its doing all the time. Of course, it will be slooooow that way, since the blindscan algorithm may not necessarily be a simple fixed frequency step loop, but can be quite elaborate. Some receivers have blindscan circuitry added on the main board, but don't have it on a 3d party add-on board, or don't have such extra feature of the add-on board supported by the STB's firmware.
Why? One of the reasons may be that people providing firmware "support" to STB importers (coders
), aren't the same people who developed its factory firmware, and simply don't know how to add and optimize blindscan algorithms (i.e. not qualified), and they're paid to do other things first.