minilab machines don't include wash steps. This is crucial if you want archival negatives!
They also run their developers at a higher temperature, in order to "push" more film through the system(faster turnaround). "Push" doesn't mean an alteration in development(say, if it was underexposed a stop), but because of the "1hr minilab" mentality, they need a faster process than the "standard" c-41 that pro labs run.
I know many pros that used to shoot headshots for extra cash before they got "big", and they took all their film to the local minilabs to get processed w/ proof prints(which were actually really good back in the optical-print machine days, those agfa machines were nice, agfa color paper was great too) Their stuff has held up fine. Not that they intended it too, but nonetheless. Now though, with 99% of people shooting digitally, film processing machines aren't getting used as much as they used to(by a BIG margin, for example: a friend of mine who owned a minilab(sold it in 2005 after 20years of ownership) said that he was running close to 1000 rolls of 35mm, 120 and 220 film through 3 processors in his shop. 3 printers, checking and color-correcting EACH FRAME. He was about quality, 1st and foremost. He made HUGE amounts of money off of simply processing film and making great prints! He had professional wedding people coming to him, cause he did a better, cleaner job on their film than pro labs they went to.
Minilab machines aren't bad, but if you want archival negs, and less pronounced grain, use the Digibase chems from Freestyle. They're really good quality, and can deliver great results. OR, use a really good lab that has lots of film running through it, use the search function here to find threads talking about it.