I agree with you on what you said but some people don't really know how to keep such achievement to themselves and I believe that since nobody knows who is who on this Forum just username, that's why the OP decided to make it look like a public announcement which it is.
Fine is good to share good news but the way we take it sometimes is not how is suppose to be.
To be frank with you, I too would like to get my first BTC and start up something as the OP did, is everyone's dream especially those who are new in Bitcointalk to get their first BTC but not everyone would make a public announcement about it, safety first.
This is why I see it mostly out of maturity (if real) seeing people showing off the amount of Bitcoin they've purchased here, why? Also, one thing that is peculiar to the people who do this is that a lot of people give them merit for it. They now follow suit, which is the only reason I believe they broadcast this kind of private transaction, nothing else.
Nonetheless, it is a very good avenue to help one's alt grow fast.
I noticed that we have many members having this same style of making post which might not be real, and you're right with what you said. These days in the Forum is like some people have to do whatever it takes to get that attention, recognition and to top it all the merit. People can go as far as to lie to get that merit or whatever their aim is.
From what you said, I don't really believe some of these achievement we see here on the Forum. Having that amount of BTC and showing it can be true but the question to the OP is "are you the owner or you just saw it somewhere and decide to let us take a look and make it look like it's yours".
Is really hard to tell who's saying the truth on the Forum.