It will get worse. The new rental reform bill is likely to ban payments up front,. which will make it very difficult for overseas students and those who wanted to avoid providing guarantors.
Additionally the Government has ignored pleas to allow fixed term tenancies for student lets. If a group of students are in a property and one or more decide to stay beyond the length of the fixed term, they will be able to. Whether the landlord has signed an agreement for next year or not.
In addition Shelter and others are lobbying Angela Raynor to do away with guarantors for those with incomes (and I assume student loans will be counted) leaving even more risk with landlords. The argument is that landlords can offset that risk byu using insurance.
A lot of landlords are selling up. A reduction in the number of rental properties will give remaining landlords more scope to select, which means reducing risk by being very careful. Students are less attractive than young professionals.
My assumption is that the long term aim is to "professionalise" the sector. For students I think that means expanding private hall provision. I think the Government should look carefully at both the German and US private rental sectors. Property owned by large investors may not be the model they really want. I recognise that many on MN don't like the concept of private landlords ( @Auchencar had a major pop at me a few weeks back) but actually at various stages in life people may want to rent, and private landlords provide accommodation cost-effectively. Equally tedious are 24 year olds who don't seem to understand that contracts may define a working relationship, but actually such relationships work best if you try and work together. Some tenants seem very aware of their rights but seem ignorant of their responsibilities, and see themselves as having the moral high ground over landlords, regardless of how they treat the property.
However in answer to the OPs question. Yes many landlords try to reduce risk by having joint and several contracts as well as guarantors. The guarantor is then potentially responsible for the entire rent, and if there is a need to chance the guarantor they are likely to go after the low lying fruit, ie the guarantor most likely to be able to pay. I would be tempted to either look into various guarantor schemes where, for a fee, a private firm provides the guarantor. OPr to negotiate. Pay rent in advance for your DC before the new act comes into force and in exchange not be required to be a guarantor. I would also drum into your DC that a contract is a legal agreement and that one of the first steps in adulthood is to respect this. Your really do not want to start adult life with a County Court Judgement against you as this will affect future rental and, quite possibly, employment prospects. I would also suggest to your DC that they collect contacts for other parents in case of emergency (and needed for that as well - say if one ended up in deep and worrying depression they would want to be able to alert parents) but emergency could also be one getting behind with rent.