There are MANY casinos that regard comps as "bonus", Grand Prive and Casino Rewards are two examples. Also, it is common for tournament winnings to be regarded as a "bonus", even where the event was of the "who wagers the most" variety. Somewhere in the back end, stats are generated to show bonuses received as a proportion of both deposits and "action". Depending on the casino and player's VIP level, they have targets for how much bonus money players should be getting on average. Where a player has exceeded their target, they will find bonuses hard to come by, but if their deposits and action leaves them below target, this will likely be corrected by additional deposit boni, free chips, and manager bonuses.
The bonuses from GoneGambling will also count towards this, and will immediately give you 50% on your first $50 deposit, followed by a percentage of your high roller deposits from $300 per 30 days. With enough GG points, it is quite possible to get bonused at 100% without even starting on the 3Dice casino bonuses discussed in this poll.
Comps redeemed with a deposit are at an enhanced rate, which is why they show as "bonus". Strictly, only the enhanced amount is bonus, but I expect the cashier cannot cope with this complication, although the back end stats probably can.
$50 every 30 days also allows entry to a number of freeroll tournaments, and, unlike Microgaming, "free" actually MEANS free!
The problem with the referral scheme is that it is based on only the FIRST deposit, which for many will indeed be to "test the waters". If anyone is in a position to refer many social contacts, it might be better to set up an affiliate site and make it your own personal site for socialising. This might, however, be a problem for US players, as both the IRS and DoJ might want a slice of your cake, or maybe even shut you down if you don't make enough