If I compare Wealth-Lab with others software (Metastock, Tradestation., pro-real time...), I see that Wealth-Lab has a limited list of technical indicators implemented in standard. Is there a particular reason ?

I'm surprise because a lot of website gives you the possibility to implement more in standard (http://www.systems4trading.com/index.php or http://www.brave.net.au/ms/list_indicators.php or http://trader.online.pl/MSZ/e-0-tytulowa-a.html).

I would like also to suggest you to create category of technical indicator because some of them work only for a list of stock and others only per stock.

Currently we have ~180 indicators in WL5 if you take the TASCIndicators and Community.Indicators libraries. (Have you installed them?)

Many more than that exist in WL4 because our users have been submitting them through the years:
WealthScript Code Library

The particular reason is that Wealth-Lab is extensible and therefore is user-driven.