TRACON Controller described a minimally spaced departure event when the Local Controller launched two successive departures possibly losing separation; the reporter advocating increased Tower separation.

Narrative

Airport was departing Runway 01 and I was working West RADAR that gets the northwest/southwest departures. There was a lot of weather to the northwest and both of our departure gates were combined into one. An A319 departed Runway 01 climbing to 40 on runway heading. I RADAR identified the aircraft and climbed him to 15;000 and left him on runway heading for noise abatement. Right behind the A319 departed a C560 was climbing to 40;000. I thought they were a little close so I didn't climb the aircraft and scanned the northwest side of my scope where I had traffic. I scanned back and thought that the A319 and the C560 were less than three miles and the C560 was out climbing the A319. I amended the C560's altitude back to two thousand. The pilot of the C560 reported he was passing two thousand but going back down. It happened so fast that I didn't know if we lost a thousand feet. The pilot of the C560 did want a turn to get out of the A319's wake. I gave him the turn and stepped him up with the A319. Recommendation; this should have never ever been any problem. The Local Controller was not trying to get the C560 out in front of a lander and they knew we were busy with the weather. This was caused the old rule of 6;000 FT and airborne. This rule DOES NOT always give you 3 miles and a thousand feet. Even if it did why would you pack two departures going out the same gate with minimum spacing? I had to give the Center more than 5 miles anyway. A team player would hold the C560 on the ground for an extra thirty seconds to a minute and this report would not be necessary. The only recommendation is brief that Towers must give RADAR 3 miles separation on departure. We briefed this before and some people may have forgotten.