1 in 6 people over 80 has dementia, according to the NHS. People need care either because of dementia, other ill-health or general frailty. The risk that a particular person may need long-term care is quite small - about 1 in 8 or 10 as best I can find out. Of course, someone with a pre-existing health condition or disability may have a higher risk than that. When I was doing this work I had a client who was a woman in her 90s, still mentally sound, who was becoming too frail to live on her own and was contemplating moving into a care home.
The figures may have changed, but then the average time between going into care and dying was about 2 years. Most people who need care don't do so before their late 80s or early 90s. 2 years fees in a good care home will cost around £100k, compared to a UK average house price of £268,000.
I still believe in the advice I gave my clients, which is that the risk that all your savings will go in care home fees is quite small, and you need to balance that risk against the cost and possible inconvenience of splitting marital assets. For example, if the surviving spouse only owns half the house and the other half is held in trust for the children, it adds an extra complexity should the survivor wish to move house.
Second marriages where there are children from the first, whether caused by death or divorce, are the exception as then you may need to split the assets so that all the property doesn't end up in the hands of the children of one spouse while those of the other get nothing. These do need careful planning.