The difference is that weaknesses were found in 3DES and MD5. Increasing computing power was not the main factor. "Only" being able to produce 2^80 random bytes is a known and expected limitation. Sure, the CSPRNG could in theory be found to have a weakness, but that has nothing to do with the 2^80 bytes and the same could be said for virtually any cryptographic algorithm.
I am not arguing that there are; that was the parent comment. However, while the 3DES weaknesses don't yield practical attacks now, they still reduce the effective key length. My point was not that 3DES is different in that it is exploitable, but that it is different from the 2^80 limit in that the CSPRNG in that the later is not a result of a mistake in the algorithm's design but instead an expected feature. Just like the fact that any fixed-size key symmetric cipher is "limited" by that key size.
Now, if someone found a lower limit based on exploiting some weakness in the random number generation, the analogy with 3DES and MD5 would make more sense.
