That wouldn't always be the case.
For example:
She clicked on new posts and scanned the list to see if thethinker42 had posted anything interesting. No. Well isn't that always the way?
We don't know if 'No' is a thought or part of the - what would you call it? - exposition?
In this case, does it really matter to the reader which? If it's important enough, tag it.
She clicked on new posts and scanned the list to see if thethinker42 had posted anything interesting. No. Well isn't that always the way?
Because the above is italicised, we now know those words are character thoughts, not just the author speaking to the reader.
If it's really important to differentiate the two, I'd lean toward a tag rather than italics.
She clicked on new posts and scanned the list to see if thethinker42 had posted anything interesting. No, she thought, but isn't that always the way?
Now, if we use quotes around speech and thoughts, it gets confusing:
"I'm going to send thethinker42 an email telling her she's banned," she said, adding to herself, "And then I shall be Queen of AbsoluteWrite!"
Gah. We agree on this, absolutely. Totally confusing.
How do we know the words following 'adding to herself' are thoughts or speech if it's our custom to put quote marks around both? Surely this would be better:
"I'm going to send thethinker42 an email telling her she's banned," she said, adding to herself, and then I shall be Queen of AbsoluteWrite!
But since it's tagged, it's not really necessary.
"I'm going to send thethinker42 an email telling her she's banned," she said, adding to herself, and then I shall be Queen of AbsoluteWrite!
Plus, of course, if we never use italics we lose the ability to emphasise certain parts of the text and make those words stand out.
Emphasis is one place I can see italics as necessary, but it could easily become a crutch as well. If you need emphasis, are you sure you have the right word, and shouldn't use a stronger one?