So what's the reason for the different treatment?
With Katrina, the federal response was an unmitigated disaster.
With this flood, the federal response is doing pretty much what it's supposed to do.
This is also not the first time we've heard this nonsense. E.g. conservatives screeched about Katrina when Sandy hit, and it didn't work -- because the responses were night and day. Instead, they lost their minds because Christie actually worked with Obama, which most conservatives vindictively mischaracterized as a "hug."
So, as I wrote elsewhere:
FEMA has been on the ground, doing its job, from very early on. They've got at least 1000 people on the ground, medical resources are deployed, they have participated in the rescue of 30,000 people, and signed up 70,000 people for federal assistance. Almost all the displaced people have moved from shelters to temporary housing situations. They've already provided over 600,000 gallons of water and 800,000 meals to the state. The federal response is significant.
Louisiana's governor is pleased with the federal response. He also doesn't want Obama to show up for another week or two, since the logistics of getting the President around would complicate relief efforts -- e.g. diverting police to cover a President's driving route would be, to put it mildly, counter-productive.
Bush's incompetence was not that it took him a few days to show up and eat some beignets. It was a failure to prepare in advance; a failure to recognize the magnitude of the storm for several days; the failure to take it seriously; the failure to properly work with state and local governments; it was a continued failed response throughout the entire episode, resulting in a disaster of epic proportions.
Let's get real. FEMA, under Obama, has performed admirably throughout his term.
Let's also be accurate about the criticisms. No one on the ground is saying that the federal response is absent, that it's compounding the disaster. They primarily want media attention, which is lacking. NOLA wants the President there to raise the public profile of the flooding; the Advocate wants him there to express solidarity with the victims.
I do think these are valid criticisms -- but they are also minor ones. It is part of a President's job to bring attention to a major disaster, and for something of this scale comfort the victims. Comparing this to the inept response of the Bush administration to Katrina, though, is mere partisan nonsense.