Yes, I see, and I remember now that the A550 (in fact the entire range of Sony's Alpha's) only have 3-shot brackets. It is a shame that Sony does not provide a better range there.
I am lucky so far, as my Lumix G1 provides the chioce of 3, 5 or 7 shots with either: 0,3 - 0,5 or 0,7 EV in between, giving me the range I need.
But on the other hand, it would need a scene with very, very big differences in hi's and low's to be needing more than 3 shot of 0,7EV. Our distinguished HDR-photographers 'vvcarpio' only has 3-shots (A350) and 'simple' only has 3-shots (Nikon D90).
Actually you need to go all the way up to the Nikon D300(s), Canon 50D and K-7 to get more bracket-shots than 3.....
Best of luck, Bruno!