i have read that we can culture yeast from commercial bottle conditioned beers, So is it not the same that we can use a bottle of our own beer that has been made from a brew that used a White labs or Wyeast culture ?
Sure, there's no reason you can't do this. Realistically, though, since you're talking about a beer you've brewed yourself, there are other times in the process where it is much easier to collect yeast.
For example, after primary fermentation is done, it is usually pretty easy (depending on your equipment) to collect some of the yeast cake deposited after fermentation. Or you could collect some fermenting wort during primary and save for reuse, or save a portion of a starter (if you use one).
However, if you want to culture a yeast from an older batch, or a batch of a friend's beer, it's entirely possible. The caveat is that you have to spend some time and effort to grow the yeast up to a usable quantity, and the surviving cells from which your new culture will derive may not be nearly as healthy as fresher yeast.
I've done it, so it's definitely possible. You just have to bear some caveats in mind.
How many batches have been fermented with the yeast? Remember that some strains tend to mutate faster than others. I've heard that you can ferment 5-8+ batches with consecutive generations of the same yeast without any problems, but e.g. Hefeweizen yeast will not be viable for that many.
What's the ABV of the beer you're culturing the yeast from? As you probably now, stronger beers will contain yeast that's either dead or in poor condition. It's probably not worth it to culture yeast from a barley wine. Darker and hoppier beers will further deteriorate the yeast too.
What yeast was used for refermentation? There are strains specifically for bottle conditioning that some brewers use. Commercial breweries very often add a completely different strain for refermentation, sometimes even a lager yeast (despite the beer being an ale). Make sure it's the same strain that was used for fermentation, otherwise you can end up with something different that what you expected.
How difficult is it to obtain the yeast you're expecting to get? If it's not a rare/expensive strain, you might want to consider either buying a fresh packet or perhaps asking your local homebrewers if they don't happen to have some extra yeast cake in their fridge.
You need some equipment and time. A bottle will have relatively few viable yeast cells, not nearly as many as a fresh packet of liquid yeast. Therefore, ideally you should have a plate stirrer, a small flask (like 250ml), a large one (2l should be fine) and a lot of patience. The culturing takes no less than a week. You should also start with a low gravity beer, as the number of cultured cells will still probably be well under what you'd normally want to pitch. After your low gravity beer's primary is done, collect the yeast cake and use that to make your desired batch of awesomeness.
Yes, that's perfectly fine, however the best way to conserve a strain of yeast that you already have on hand is by making an oversize starter and saving a portion of it or slanting the yeast. this way you prevent most of the problems that comes with yeast reutilization from batches, like contamination and the pain of isolating a pure colony of yeast.