I will never buy a business, real estate is a much safer bet.
To be fair, almost any software based business could be irrelevant in 10 years.
First is the large capital outlay as compared with a small web project, which means many more eggs are in that one basket.
Second is the slow turnover, which means that you may be waiting for years for a good property (since if it's a good property, there are only a few situations where the owner would sell), and if you choose poorly, you will be stuck with the poor property for many years (as no one would want to buy it).
Third is you will still have to watch out for your property becoming irrelevant, for example for a retail store, either due a downturn in the trendiness of the neighborhood driving out business, or perhaps undesirable construction in the area (e.g. a mall across the street that takes all your foot traffic).
Really the safest way to invest in real estate is through REITs, where the risk is spread across many properties.
Perhaps I'm naive, but I think your risk in buying a business goes down if the current owner under-appreciates what they have, and you have the skills to do it better than them.
This is completely true, my sentiment is more for the idea of a "turn-key business" acting like an annuity. I don't think every business for sale is going down but I think there's a large enough risk case that I'd rather avoid it.