When you sponsor any immigrant these days you have to sign an I-864. That document specifically states that "a sponsor's obligation continues until the sponsored immigrant becomes a US Citizen, is credited with 40 qualifying quarters of work, departs the US permanently or dies."
I don't know where the 2 year guarantee number came from. This is a 10 year guarantee IF your sponsored immigrant works for all those ten years.
It should be noted that you are liable to reimburse the government for welfare benefits, so it is not like that is a ton of money (you are far more likely to be forced by a divorce court to pay more in alimony or child support).
Secondly, I totally disagree that having applied for a tourist visa has no impact on the K-1 visa. They may tell you that, but that is utter nonesense. The consulate is very careful about visa fraud since the DR has one of the highest rates in the world. If you have already been denied a tourist visa they put your application under extra scrutiny (more then even the incredible amount they normally do) since they will make an assumption that the person was denied one visa and is trying to get another one as a result. They will question their motives and stall as much as they can in issuing the visa.
Unlike the US where you are innocent until proven guilty, in the immigration process you are guilty until you can prove yourself innocent.
BTW- if you want to see a copy of the I-864, you can download it from here:
http://www.ins.usdoj.gov/forms/download/i-864.htm