The benefit of having this sort of care in a retirement setting are great - firstly, if someone goes in when they are not impaired, and this care is possible, they can stay in their familiar setting with people they know and trust. It is easier on the resident and the family. Secondly, retirement homes have higher functioning people than long-term care in general so the activity and stimulation is greater for that person. This may translate into a slower decline than if they were in a home with very limited activity and programs. Thirdly, because of the cost factors involved, there may be extra resources for those with dementia in a privately funded retirement home than there is available in publicly funded long-term care homes. There are many retirement homes that have excellent care and resources for people with dementia.
However, as beneficial as it may be, there are also potential issues if the security is not adequate to prevent wandering or the staff are not equipped to manage the resident's issues. By and large, most retirement homes are very up front with families about their abilities to manage people with various medical issues. Beyond liability issues for that one person, they need to ensure the safety of their other residents and staff. While it would be great if the options for care for those with dementia increased (which it no doubt will over time), I respect and applaud homes that recognize their limits and do not take on people who they cannot safely look after.
All of this aside, while the setting itself might be nicer in a retirement home than a long-term care, it is not always the best place for someone with dementia. Each situation is different but one needs to carefully assess staffing, training and environment in light of the person's deficits. Clearly, for many cost is the prohibitive factor in the choice of care simply because those on government pensions alone would never be able to afford a private care setting (but that is a topic for another time). However, for those who can afford retirement or private assisted living, it is not a 'given' that it is the best place for your loved one if they have cognitive impairment. As with any sort of care for a senior, one has to take the time to look for a place that can meet their needs now and in the future at a price they can afford. Shop around, ask questions, tour, try the food, get references, etc. Because the person with memory impairment is particularly vulnerable, great care needs to be taken when choosing a home to relocate them to. As with anything, the best and most appropriate home isn't always the most expensive or fanciest. In some cases, the most suitable option for someone may indeed be long-term care.