I agree with zuzu that I am not fond of looking at mulch. I would think rose spacing would have a lot to do with both the natural size of the rose and with the resources. Here in AZ, where it is dry I think there is a tendency to space plants further apart than one would do where the soil remains damp.
I would imagine climbing roses get planted at intervals not usually closer than 4 or 5 feet apart. I think at Roseraie de l'Hay the regular spacing for climbers was closer to 8 ft; but the constraints there may have been more architectural than they were agricultural. Minis might easily be placed 12 to 18 inches apart, if the plants are compact as the flowers. Some floribundas remain smallish, and I think two feet apart could be great for them. But others stretch out to five feet across. I like the idea of planting hybrid tea roses in beds closely together, if one can get away with it. But there are monsters like Folklore that might seem crowded at three ft spacing. And if you like to mix other plants with roses, sometimes the spacing can be much more open, too.
Of course, rose collectors (we know who we are...) might plant roses close together simply to enable us to build a more comprehensive collection.
So it all depends on your roses, on your tastes, on your geography, and on your planting plan.
