It is entirely correct, because capital allowances aren't a deduction in arriving at income for USC purposes (and if you look at the tax return you'll see they are entered separately from the net rents). A lot of people avail of capital allowances (on industrial buildings etc), as a means of sheltering their rental income and thereby avoiding tax. The whole point of the USC is to widen the net, and charge income that otherwise was going untaxed.
Ditto with your P60, if you have a pension / PRSA / permanent health insurance contribution going through payroll, then while you may be getting a deduction for income tax you will still pay USC on it.