Not quite right. Miners can and will mine things with a lower fee. Many nodes will simply not forward the transactions however.
For low-priority transactions, it doesn't look to me like many miners are accepting lower fees.
Right now, a 999-byte transaction paying the reference-implementation-default fee of 0.0001 BTC will wait 2-3 hours to get into a block.
A typical 250-byte transaction paying the default 0.0001 BTC fee will see its first confirmation in 5 or 6 blocks (about an hour on average). If you want your transaction to confirm quickly, then right now you need to pay about double the default fee.
Some results running https://github.com/bitcoin/bitcoin/pull/3959 (more review/testing welcome) :
Code:
$ for i in {1..25}; do ./bitcoin-cli estimatefee $i; done
0.00077821
0.00044643
0.00044444
0.00044248
0.00044248
0.00038911
0.00038760
0.00026810
0.00024752
0.00022831
0.00020040
0.00017513
0.00016155
0.00014706
0.00013802
0.00012531
0.00011779
0.00011013
0.00010363
0.00010111
0.00008905
0.00008636
0.00007474
0.00006743
0.00004444
0.00077821
0.00044643
0.00044444
0.00044248
0.00044248
0.00038911
0.00038760
0.00026810
0.00024752
0.00022831
0.00020040
0.00017513
0.00016155
0.00014706
0.00013802
0.00012531
0.00011779
0.00011013
0.00010363
0.00010111
0.00008905
0.00008636
0.00007474
0.00006743
0.00004444