1. I am sorry to say, I prefer a to b. 口语特点,用逗号停顿代替 that, I prefer a to b 为 say 的宾语从句。I am sorry to say, I prefer a to b. = I am sorry to say (that) I prefer a to b.
2. I am a dog, I eat meat. 无法与上句相提并论。这是并列句,缺少并列连词,改为:I am a dog, and I eat meat.。那个是主从句,是用逗号代替了从属连词 that。