Of course they "can" be, but they are often not.
I'm an internet retailer and I have to deal with this all the time. I go through this at least once a week with customers who use debit cards, and I can tell you from 15 years of experience that these holds often take 10 days or more to be released. I have to waste my time explaining to people that there is nothing I can do to release the funds back to them quicker and they need to call their bank.
That again is not the banks fault. Most of the time it's the provider for your merchant services that is sitting on it.