Receivers did not have a short lifespan until a few years back. I almost feel like all the new digital processing and connectivity options appear to be a scam devised by the manufacturers to force consumers into upgrading their equipment more frequently than before.
First, there were stereo receivers. These were the state of the art, both for audio and video for a long time. THen Dolby Surround came out and started the rapid proliferation of surround options: 5.1, 6.1, 7.1, DPII, DPIIx, THX, whatever.
A video input was initially added to receivers to decode surround info from the video signal. The number of video inputs started quickly growing and receivers became video switching devices as well. Now we have S-Video, Component Video, DVI, HDMI, etc.
Similarly, receivers used RCA jacks for connecting to other equipment for a long time. Then optical and coax digital connections to CD players were introduced. Now we have HDMI, FireWire and a few other proprietary technologies.
There has been a few fundamental technological improvements, like the new digital amps, but these appear to provide cost, power consumption and form factor improvements.