I would imagine that prior to this August it was not the case but will certainly be the norm for the short to medium term. It should probably always have been this way. This is simply a reflection of the banking sector having to decrease it's risk exposure.
I have an agency with PTSB - my understanding is that giving interest only is determined by loan to value - less than 90% and they will give you a period of up to two years interest only on your own home. For investment properties interest only for full term is allowed
Not sure what the norm is but you could check out what the opposition is offering eg AFAIK Bank of Scotland Ireland ( Halifax ) offer interest only mortgages on a ppr with flexibility as to when the principal is repaid. Also there is a crowd called Mellon mortgages who advertise interest only products on pprs in the Sunday Business post regularly. ( might be a Bank of Scotland product )