Intel was vulnerable to Meltdown and Spectre. AMD was only vulnerable to Spectre.
Meltdown arose because vulnerable designs delay memory protection checks until as late as possible, after illegal accesses could have already affected state. This is a questionable decision, as it is playing fast and lose with the most fundamental building blocks of security. Most companies wisely chose a more cautious approach.
If an investigation found that watermelon is carcinogenic, that would be a problem. If that same investigation found that Andy's Farm sells watermelon that contains benzene, Andy's Farm couldn't defend itself by saying all watermelon is carcinogenic.
Meltdown arose because vulnerable designs delay memory protection checks until as late as possible, after illegal accesses could have already affected state. This is a questionable decision, as it is playing fast and lose with the most fundamental building blocks of security. Most companies wisely chose a more cautious approach.
If an investigation found that watermelon is carcinogenic, that would be a problem. If that same investigation found that Andy's Farm sells watermelon that contains benzene, Andy's Farm couldn't defend itself by saying all watermelon is carcinogenic.