The Rane MP4 came out in what... 2005? I'd say supporting it up until ~2011/2 is a decent product life for a digital product with software support... Version 2.2 of Scratch Live can still be downloaded which was the last supported version. Problem is as time goes on the hardware and connectivity doesn't keep pace with the demands of the software... if the software outpaces the aging hardware it will start to perform poorly and users will blame the software not their own reluctance to upgrade. EOL/Discontinuation is the only option a company has. The SL1 and TTM-57SL both got 10 years of new updates... I'd say as far as supporting aging hardware goes Rane and Serato are both pretty top notch.
When users of the newest hardware can't get new features because the software needs to continue to perform on decade old hardware that's bad business... eventually you need to kill off the old so the new can move forward in technology.
You can see the reluctance of DJs to upgrade in the software requirements though... most DJ software still lists the Intel Core 2 Duo which is an 8 year old chip as the minimum system requirement.