The notions that 2005 and 2034 are "prophecies" are a little bit of a stretch. It doesn't compare to the 1914, 1918 and 1925 predictions at all. Even 1975 is more credible, even though a devout JW will say that the WTS never claimed 1975 as the date for Armageddon.
I think that they use dates like that to scare people into thinking that the end is really close, but they don't commit to a date. If it happened in 70 years in John's time or 120 years in Noah's time, then we "have" to be close to the end, "if" the Gentile Times ended in 1914.
Not that it's any better or acceptable. They still use dates and numbers and predictions to scare people. Now, instead of naming a date, they keep it elusive....it can happen anytime. In some ways, that's more scary than having a date set several years out. They got busted for date predicting, so now they can claim to not predict dates, and it's worked in their favor. Now they can try to scare people that it's "imminent".