It's not exclusive to tournies. However, the gap concept in tournaments is much more than just the concept that calling with AJ against the range AJ-AK is -cEV; it is strongly affected by the fact that sometimes cEV and raw EV are nowhere near linearly related. During these times the chips in your stack are worth more than chips in the pot. This makes tighter play in general more correct (although, usually you will have at least some players at your table who do this too much, such that playing against them aggressively becomes correct). However, it also makes variance in chips -EV, i.e. plays that either cost you many chips or earn you many chips are actually less profitable than plays with the same cEV that either cost you a few chips or earn you a few chips. Calling is higher variance than raising because raising carries FE (which is small risk, small reward). Therefore, the gap concept is strengthened greatly in tournaments on the bubble (and to a lesser extent, throughout the tournament).

Another interesting effect of the gap concept is that it perpetuates itself if your opponents know about it. If your opponents are calling tightly, you should raise more liberally.