Maybe Apple is limiting features to get people to upgradem but I doubt it. More likely, there is real reason for each one.
1st, the iphone 4 will still run iOS6 and its a 2 year old phone, 3 years when iOS6 comes out, with a processor that is 2 generations behind assuming the next iphone will debut with iOS6.
No flyover/turn by turn: Its processor intensive. You still get maps, and the same views you always had.
No Siri: Iphone 4 never suppprted Siri.
No 3G facetime: this one sucks, but I imagine its to prevent network overload from giving it to both phones. Might have been part of the deal to allow it. Regardless of how you feel, legal 3G facetime video calling is a big deal and it must have been tricky for Apple to negotiate.
Is it planned obsolensence? Maybe. But I think its silly to think Apple is still going to try and roll features out to 2 year old hardware and push it past its limit. Its a phone, not a computer.
All my apple products have lasted longer and had way more OS updates than any of my non Apple gear did back in the day. I used to be jonesing for a new phone after 1 year and a new computer after 18-24 months (and thats with fastidious care). My phone is 2 years old, I feel no need to upgrade, my laptop is 2 years old, and going strong and will be through Mountain Lion.
Complain all you want about "planned obsolesence"; my experience has not been that; Apple stuff support is pretty consistent as long as you stay somewhat current. And if you have old stuff, the cut offs are clear. There is no mucking about trying to get Airplay on G4 cubes and such.