porch level with indoor floor?
If your porch is entirely roofed and screened, then you probably don't need to worry about it. But that really depends on the size of the porch and roof. If wind driven snow can build up against your door, then you're likely to have a problem with melting snow. The water can, and will, find its way in. And the water that doesn't find its way in may refreeze and create an ice build-up. There's always going to be just enough warmth from the inside expressing its way out under the door, and it can be enough just to create a problem with the snow. If snow can't possibly get to your door because the porch walls and roof overhang are just too far away, then you may be OK.
If what you're talking about is simply a small overhang under which one or two people can stand in the rain, then the step is by far the better way to go.
As for accessiblity, renovations to existing homes requiring that kind of accessibility can include a ramp to get from floor to floor. New contruction should attend to those problems as outlined above.
[This message has been edited by treebeard (edited December 30, 2003).]