I got my 360 as a present, and I've loved it since. Dead Rising also helped, a lot.

PS1 - decision made for my family by my parents when I was 5.
PS2 - because PS1 had never let me down
PS3 - because PS2 had never let me down
Vita - because I wanted to play LittleBigPlanet; Gravity Rush & WipEout 2048.
PSP - because I love my Vita.
GC - because it was £30 with 4 games a few years ago and I thought that was a really good deal
Wii - on the promise of Pikmin 3 and because the Mario Galaxy games looked ace
GBC - Pokemon.

PS3 and 3DS - Have tons of exclusives that appeal to me. Games or the promise of games is always the biggest reason for me.

PC: RTS games, League of Legends, The Witcher series.
PS3: Used to the controller, the 1st party games, owned the two previous consoles.
DS: I loved the first 3 pokemon games so much that i got it to play soul silver. I want a remastered pokemon rub/emerald for the 3ds.

NES - Mario

Genesis - Sonic

Sega CD - Sonic CD

Dreamcast - Fighting Games. (Soul Calibur, CVS2, etc.)

Game Gear - Portable Sonic awesomeness.

PSP - Because it was cheap and I just wanted to own every system that gen.

PS1 - Final Fantasy VII commericial.

PS2 - RPGS.

Original XBox - Online platform, Halo 1 for system link partys, Halo 2 for online awesomeness. All that Sega love at the time (Panzer Dragoon Orta, Toe Jam and Earl, Shenmue 2 US version, etc.)

360 - Staying with MS in the next gen. Online experience again.

XB1 - Sticking with MS again. Halo franchise and another awesome online experience.

Wii - Nintendo games.

3DS - Nintendo games, and being the best handheld system on the market.

PS1 - When I was 8, mom suggested we get one
PS2 - After PS1, how could I not Tekken 4 and GT3 were my first reasons
PS3 - Continuations of many PS2 series. Expectations of lots of JRPG's.
GC - Tales of Symphonia, SMS, MKDD, Baten Kaitos games, superior versions of PS2 multiplats
Wii - Xenoblade, TLS, other JRPG's on it, Mario Galaxy games, Metroid Prime 3
PSP - Crisis Core, Ratchets, JRPG's
DS - Ninty first party, good 2D games, JRPG's

edit: forgot Genesis and Saturn.

Same reason for both. A lot of 2D side scrollers on each, and SHMUPs are the best of their respective generations.

I own basically every major console and handheld since the NES, solely because of exclusives. Well, except for Sega consoles. I did own a gamegear though.

I usually get the console with the JRPGs that I want to have. That is why I got the 360 first before they stopped supporting JRPGs and then a PS3 followed by the Wii.

My DS and PSP were hand-me-downs. I got the older models while my sibling enjoyed the newer ones but then I got my PSV as a gift. So it was all good in the end. lol!

I usually get Sony and Nintendo consoles! The reason for Nintendo ones are the exclusive Nintendo franchises. An Sony for some first party and the third party!

Because of controller, games and all my friends have a 360.