AUS Departure Controller described minimal departure separation provided by the Tower; claiming Tower Controllers were not complying with local/national directives.

Narrative

While working RADAR East (RE) I observed what I believe to be an Operational Error (OE). A Regional Jet departed Runway 35R heading 010 climbing to 4;000. Then Aircraft X; another Regional Jet; departed Runway 35R right behind the first heading 010. Then another civilian aircraft departed Runway 35R right behind Aircraft X. This aircraft appeared to be heading 350; but eventually turned northwest. The first Regional Jet and Aircraft X were both assigned the same initial route of flight (CWK4 departure with ILEXY or HOOK transition on the same radial out to the airspace boundary). The AUS/ZHU LOA requires that I provide ZHU with 5 miles constant or increasing. Aircraft X was less than 2 miles behind the first Regional Jet. When Aircraft X checked-in on my frequency; the pilot indicated that he had been assigned 210 KTS by the Tower. This speed restriction was obviously done in an effort to prevent an overtake situation on departure; or to allow the first Regional Jet to pull away from Aircraft X. I do not know if the Tower was utilizing Visual Separation between these departures. The ceiling was around 2;800. I do not recall if the first Regional Jet was assigned a diverging heading that was different from Aircraft X; but it appeared that both aircraft were on the same headings. Aircraft X was already above 3;000 by the time I observed this situation; and I did not feel that it was safe to turn Aircraft X to the left because of the civilian aircraft that had departed right behind Aircraft X on a diverging course. Local SOP does not allow me to turn Aircraft X away from the departure course -- only towards the departure course. I did nothing until the first Regional Jet had climbed above 4;000 and increased the distance between the succeeding Aircraft X. I called the Tower and asked if they were busy; because there were no aircraft on Final to Runway 35R; and I was unsure why the Tower was in such a hurry to get these three aircraft airborne with minimum (or less) spacing to the departure sector. Aircraft X was assigned 210 KTS as a departure speed restriction by the Tower; and this is contrary to FAA Order 7110.65. Additionally; this speed restriction was not forwarded to me by the Tower. This is an example of AUS Controllers believing that they are helping the pilots; when in fact; they are not applying the SOP's; LOA's; or national directives appropriately. This is not ORD; DFW; ATL; or LAX. Why are we conducting business this way? Recommendation; I could have helped the situation by turning the first aircraft earlier; or by issuing an 'expedite' clearance to the first aircraft. Additionally; I could have assigned 3;000 to Aircraft X in an effort to prevent the situation from getting worse. There was no need for the Tower to run this type of operation. There was not a string of 30 departures at the runway waiting to go -- only these three aircraft. We need to get back to the basics of running a safe operation; and looking out for the Controller in the next sector. As a Departure Controller; I should not be required to prevent an Operational Error on initial contact.