Firstly I asked if you expected your desktop to last 20 years, you responded "yes I expect my desktop to last 10 years", nice way to move the goal posts. A 1994 top of the line desktop would be using a brand spanking new 100Mhz Pentium Chip running Windows 3.11. What exactly would you apply this powerhouse to today? Now because you (and a small handful of people) are running 15 year old machines to perform some specific task, everyone is supposed to pay more to provide you with ongoing support and spare parts? For a 20 year desktop lifespan, Microsoft for example would need to write Windows 8 to be able to run on an original Pentium (with FDIV bug), or support every version of Windows from Windows 8 down to 3.11 (an OS that didn't even have an IP stack). Tell me who gets to pay for these armies of developers?
I'd argue that the 3GS IS horrendously obsolete. While the it can up upgraded to iOS6 there are several features that do not function (VIP list, Offline Reading List, Shared Photo Stream, Siri, Maps flyover, Turn-by-turn navigation, FaceTime on 3G, Hearing aid support). It does not support iO7 (Control Center, Notification Center, Air Drop, Improved multitasking, upgrades to camera and photos, iCloud photo integration, significant upgrades to Safari, Find My Phone, Car Play, plus a bunch of stuff to support enterprise usage). Oh and iOS8 comes out this fall. The 3GS doesn't support LTE, HSUPA, nor 802.11n. The iPhone5 has 4-8 times the processing power of the 3GS, 4 times the memory, 8-12 times more powerful video processing, the camera has 3 times better resolution, does HD video, image stabilization, includes a front facing camera, plus the battery lasts longer too . This all within 5 years (technically only 4 as the iPhone5S came out in 2013), now imagine a 20 year old smart phone.