Well, you would not really fully hinder their choice, more like partial hinder their choice. True, if a HMV gift voucher was given, you are limited to buying whatever HMV sells. If WH Smith gift voucher was given, you're limited to whatever WH Smith sells. So yes, technically you are right, you hinder their choice. But on the other hand, if you give an Argos gift voucher, you do not really hinder their choice, because they have a whole catalogue to pick from, compared to having their choice hindered by what you pick. For some, it is better than being given what they don't want.
For example: "Here's a present from me to you." The person opens the present and finds a jumper. The person have to put on a fake smile so not to hurt your feelings, but is thinking Oh great! A ruddy jumper! The person may feel you hinder their choice, because their choice is limited to a jumper.
I would not think of gift cards being totally hindering my choice. It would feel like a trade-off. Okay so I am limited to M&S, but at latest M&S do sell food as well as clothes. Okay so I am limited to HMV, but they do sell headphones, not just only CDs and DVDs. Okay so I am limited to Argos, but hey, they have a whole catalogue so I have a better choice. Better than given a reindeer jumper and I feel like wanting to say "Have you ever seen me wear a jumper at all? I've always worn a sweater but never a jumper!"
As for vouchers becoming defunct, they do have to be used within a timeframe, usually 1 year. But if you still have not yet made up your mind what to buy, you could just add extra funds on it to keep it active. For example: If I was given a M&S voucher worth £30 for Xmas but find nothing useful. I could wait 6 months later and try to see what they've got for summer. If still nothing useful, I could decided to add my own £20 on top of the card (bringing a total of £50), but when I made a top up, the active timeframe kind of renew, so card have to be used within a year from the time I top up. It is possible to keep a card active just by adding a bit of more on it. This also helps keep it active until when the shop have an item of interest.
As for shops closing down. True, it do happen, but you could always stick to well know companies that you know are strong enough to stay in business. For example, go for M&S, Argos, etc., But don't risk buying from shops that had sometimes been on the news about being in the red. BHS, House of Fraser.