Isolating just the network fee — not the total cost of a purchase — shows a simpler picture: USDT, TON, TRX, and ETH each ride on a different network, and each of those networks charges its own fee to process a transaction. That fee can be small or larger depending on congestion, but it's a separate number from the Stars price.
The network fee is the closest crypto equivalent to a card's processing cut, except a card's cut barely moves while the fee on USDT, TON, TRX, or ETH gets recalculated by current network conditions each time a transaction goes out.
None of these four networks fixes its fee in advance — congestion at the moment of payment determines what USDT, TON, TRX, or ETH actually costs to send, separate from the Stars price.
The fee is the only part that actually varies by asset — the Stars price doesn't, so comparing fees in isolation shows what's really changing between USDT, TON, TRX, and ETH.
It can, particularly on Ethereum's base layer during busy periods — though that's a matter of current congestion, not a fixed rule.