Nothing's 'changed'. Safety has always come first, if you have an issue you can't launch. I suggest you look back over the 30-year program and see how many times a launch has scrubbed or delayed. A great number have. Perfect launches like STS-129 are an exception to the rule. We might look back with rose tinted spectacles at previous launches and think this stuff all used to go off flawlessly but the truth is launching rockets, and especially vehicles as complex as the Space Shuttle, has never been straightforward.
Thew GUCP has been a bone of contention on numerous previous occasions, sometimes it just doesn't seal properly.
The design of External Tank hasn't changed since STS-96 or something (the first use of the lightweight variant) and the stringers are a known problem, and have been repaired before (although not on the pad to my knowledge). This isn't an issue they can't repair, but would you rather they repaired it and everything was safe, or the ET (which takes most of the strain of launch) broke?
The flight deck panel and breakers they replaced are just old. Discovery has been going a long time and hasn't been refitted for some time.
All the Shuttle craft are the same way, just look at the outside tiles, the paintwork, the number of tiles that have been replaced underneath...
The complexity of the beast means stuff sometimes doesn't go to plan. Safety is the byword, and NASA ans United Space Alliance stick to it. I prefer it that way.
As for Soyuz didn't the most recent one have a delay? Also it's a very much simpler vehicle in a part of the world where the weather is very stable. The USA don't have that kind of luxury, but in return we get to see a few more flights of one of mankind's most amazing pieces of ingenuity... if we're patient.
I know it's frustrating, and I also watched a great number of friends on Twitter gather excited in Florida for the NASA Tweetup, some spending lots to get there, only to see them get no launch. If you feel bummed out, imagine how they felt! But all of us hold no gridge or place no ill will because we know it's all done for a reason.
STS-133 will fly, but only when it's ready.
