No, nothing at all wrong with using ordinary laundry detergent on your fleece garments. Years ago, it was sort of conventional wisdom that liquid detergents could damage Gore-Tex clothes (owing to the surfactants, or “surface-active” substances, previously used in detergents, now no longer the case). I suppose from that, I can see how the warning, “Detergent may damage Gore-Tex,” progressed to, “Detergent destroys all outdoor clothing.” That’s just the nature of information dissemmination聴people tend to add their own little interpretation, and before long black is white and vice versa.
But I digress. All outdoor-clothing makers put their products through pretty rigorous in-house “wash tests,” using ordinary washing machines and detergents that comsumers are apt to use. It’s true, there are some detergents out there now that are purpose-made for outdoor clothing. As you note, Nikwax Tech-Wash ($8.75; www.rei.com) is designed for fleece or waterproof-breathable garments, and is meant to leave less residue than ordinary detergents. And it probably does, but to what extent the ordinary person would notice I can’t say.
The one thing I can recommend is that you not use fabric softeners or those sheets you toss into the dryer. These most definitely leave a residue, particularly the sheets, which spread a very thin layer of waxy material over fabric. Sure, it leaves a pretty smell and reduces static, but it also inhibits the wicking ability of the fabric.