This is happening with all tablets and mobile devices. It's not just a Microsoft thing. It's a rapidly developing market so this is bound to happen.
Apple has done this with most of the iPad releases being less than a year after the previous release and even discontinuing some models within several months of announcing them.
In the most technical of senses, you are correct. But realistically, you are not correct.
1st generation: April 3, 2010
2nd generation:March 11, 2011 (3 weeks shy of a year after 1st gen)
3rd generation:: March 16, 2012 (1 year after 2nd gen)
4th generation: November 2, 2012 (8 months, Apple caught a lot of grief for this)
Air: November 1, 2013 (1 year after 4th gen)
Only the 4th gen came out less than a year (3 weeks between 1st/2nd is not significant)
My mom bought a Kindle Fire (which she had constant problems with) and she was pissed when the Kindle Fire HDX was released several months after. Mostly she was pissed because the issues were fixed in the HDX and she was stuck with her problematic Fire. Android tablets come and go so fast I can't even keep track of them.
People had the same issues with PCs and laptops up until just the last 5 years or so. This is just how it is with emerging technology. As long as your current device still works and is supported there is no reason to get upset about it other than gear lust.
There is a difference between when a person purchases a device shortly before the next generation is announced and the announce dates between generations. What I've been talking about is the company's timing of announcing generations.
Kindle Fire - 1st generation: November 15, 2011
Kindle Fire HD - 1st generation: September 14, 2012 (10 months after KF)
Kindle Fire HDX - 1st generation: September 25, 2013 (1 year after KF HD 1st gen)
Kindle Fire HD - 2nd generation: October 2, 2013 (13 months after 1st gen)
Surface Pro 2 : October 22, 2013 (this doesn't factor in the low inventory available in the 2 months or so afterwards)
Surface Pro 3: May 20th, 2014 (7 months after 2nd gen)
Both Apple and Amazon have a pretty steady release cycle. The exception was Apple releasing the iPad4 8 months after they released the iPad3... and they caught a lot of flack over it... including threats of a class-action lawsuit. Given that many here believe that the press and customers are overly friendly to Apple, that criticism is quite remarkable.
So here is Microsoft announcing the SP3 7 months after SP2 and "all is good, that's the way technology goes". mmm, ok.
I'm not saying that I am upset. I have a Surface 2 and no plans to get an SP3 (until the app gap is closed). What I AM saying is that if people are upset at the short time between generations, it is understandable because contrary to what you said, it is NOT the norm.