I heard someone, (I won't mention who) on another discussion forum say that Colt AR15 rifles are NOT MIL-SPEC and that other brands such as Bushmaster are superior.  Is this really true?

Each brand has it's own supporters, with valid reasons for their choice.

I have both Colt and Bushy carbines and, considering mine which are both excellent specimens and others I have handled, I prefer Colts, finding them to be superior in fit and finish.

Colts have non milspec firecontrol parts which are easily obtainable. IMHO this is of limited to no significance in a civilian rifle.

Colts, except their M4 type variant, do not have chrome lined barrels. Put a check in the "con" box for that one.

Colts are somewhat more expensive but are easier to sell. I know you'll "never" sell your rifle. Never say never.

Colts are historically significant as well.

Will you go wrong purchasing a Colt or rifle from other reputable firearms manufactures? No.

[b]There is no AR-15 type weapon that is available to the civilian population that is Mil-Spec.[/b]  [b][size=4]NONE[/b][/size=4]

Colt is generally a little further from some Mil-Spec's than other brands.