Not to be an apologist but I've only ever heard the first part - that they strengthened the S-boxes against differential cryptanalysis at a time when everyone else was still 10 years away from discovering it.
If you mean with the second part that the key was shortened from 64 to 56 bits then that made it easier for everyone to brute force it, provided you had the resources.
Yes, it made it easier for everyone, however, because the NSA had a lot more money to throw at the problem, they could do such years ahead of anyone else. Also, the NSA originally was trying to get IBM to use a 48-bit key; 56 bits was a compromise.
The Technical Director of the NSA Information Assurance Directorate gave a less sinister explanation for this in a keynote talk[1]. It was dropped from 64 bits to 56 bits for two reasons: 1) they wanted to add 8 parity bits to make it more robust for tactical military use, and 2) they decided that 56 bits would be an acceptable key length to only last for a couple decades before it would have to be replaced. They had no way of knowing in 1976 what advances in cryptanalysis would be made over the next several decades, and wanted to make sure that the public wouldn't be tempted to rely on any one particular algorithm longer than was necessary.
This might seem counter-intuitive at first, but remember that the biggest threat to NSA cryptography was from Soviet cryptanalytic work, not from the public sector. Public researchers would publish any advances they made. If the Soviets cracked DES there wouldn't be any public notification - they'd just siphon off sensitive data for years until they were caught.
If you mean with the second part that the key was shortened from 64 to 56 bits then that made it easier for everyone to brute force it, provided you had the resources.