It is kind of accepted, and thus not dwelled upon when writing articles. It would be the same thing as trying to define every term in a paragraph as it's written. Pretty soon everything bogs down in the description of the details and the meaning of the total document is lost.
Every astronomer knows what you are describing, that yes, potentially many of the objects we observe now may no longer exist, and we wouldn't know for thousands or even millions of years that they didn't. And of course it's not just existence, but anything we know about them determined from its light/EMF signals.
These are difficult concepts to grasp, but reality is what it is. We can see now what we can see, but yeah, what we see is really much older or back in time, if you will. We know that 'local' objects are fairly concurrent, time-wise, with us. But even in the case of the nearest stars, we wouldn't know if they 'blinked out' for several years. Hell, sunlight takes 8 minutes to get here. 
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