chests& keys

can anyone tell this level 15 newbie {W/R}: why on earth I would continue to buy keys and open chests at a serious loss of gold each time?

Elwood

Later in the game when the chests are of better quality or you are in Hard Mode it can be profitable. Chests are kinda like playing the lottery. For the most part and over the long term, you lose money, but you can every once in a while get a very rare item that is worth it.
Also, there is a title (treasure hunter) for opening any chest that have keys that cost more then 600g. Some people are just obsessed with getting titles.
ALSO, well, for a lot of people who have a ton of money, what else are you going to spend it on besides that or vanity items like minipets or armor? It may see unfathomable to you, but many people can easily afford to spend several million gold on worthless things like lockpicks or sweets.

The wiki has some detailed (perhaps more detailed than you're looking for) information on lockpicks and odds.

http://wiki.guildwars.com/wiki/Lockpick

As Hawk alluded to above, using lockpicks when you're still just starting out on lowend chests is probably overkill. They can start to pay off once you're in areas where chests require costlier keys; although, the costlier the chest, the lower your odds of keeping the lockpick.

If you don't care about the titles, then I'd say do without lockpicks or keys. Odds are a chest that needs a key will give you merchant fodder. Personally, I love lockpicks because I can't stand not looking in chests, and lockpicks mean I don't have to keep stacks of different keys for each area.

Bottom line: it's a gold sink. It can also be a fun gold sink, if opening chests and hoping to see gold text is your thing. Low level chests are almost unilaterally not worth dealing with, unless you're trying to max Lucky on a bunch of 90% retain chests.

Reasons to open a chest:
Get treasurehunter title
Helps with wisdom title
Add to Lucky/Unlucky title
Hope for a pretty gold, opening chests in places like Doa, UW, FoW or Echovald Forest/Raisu Palace, or other areas with rare drops, can be more rewarding.

All above it's true and IMO two other thing are very important:
- it’s FUN and thrill ("and what I will get now...")
- unlocks things for PvP - of course if You are interested in PvP.