RC/RL circuits and frequency selection
There is a lot you implied or are assuming that you didn't state.  The order of two components in series only matters if you access the node between them.  It doesn't matter either if they are in parallel.  You really should be more careful in explaining what you are talking about than just "RC and RL circuit".  There are many ways to hook up resistors, capacitors, and inductors.

You apparently mean the special case of a RC and RL circuit where the two components are used as a frequency-dependent voltage divider.  In that case the order matters just like it would if two different resistors are used in a voltage divider.  Clearly these two circuits are not the same:



If the 10 k&Omega; resistors were replaced by capacitors, it would be even more obviously not the same.  For the purpose of analyzing R-C filters, you can think of the C as a resistor that goes down with frequency.  If R1 were replaced with a capacitor, the voltage divider would attenuate less at high frequencies and more at low frequencies, which we call a high pass filter.  At DC it would attenuate infinitely, meaning it blocks DC.  Similarly, if R3 were replaced by a capacitor, the voltage divider would attenuate more at high frquencies and less at low frequencies, which we call a low pass filter.  At DC the capacitor looks like a open circuit, so it wouldn't attenuate at all at DC.

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