I don't believe that the machines are becoming tighter, per se, just that they are becoming more expensive. I don't pretend to know what kind of machine you like to play, Nathan, but what I do know is that several new machines (especially at the penny denomination) don't necessarily have the capability for you to directly choose how many lines you wish to play and how much per line.
For example, if you're satisfied playing twenty lines at a penny per line, then you would only be looking at a $0.20 total bet. American Original machines, the old school ones, are such that you only have to bet a total of a penny if you can tolerate that, (YUCK!) by betting only one line at one credit per line!
However, many of the newer machines that are coming out seem to be more expensive. You have games like Yardbirds, Antony & Cleopatra and whatever the hell else is on those banks upon which I believe the minimum bet is $0.50 for all games. You have some Quick Hit machine with what appears to be three games on it (but a bonus that applies to all three) that is a, 'Penny,' machine, but the only possible bet amounts are $1.00, $2.00 and $3.00. You have Buffalo Gold upon which the minimum bet is $0.60, and the new Buffalo machines with the Progressive upon which the minimum bet is $0.75 (as I recall) and one must bet $3.00 or $3.75 to qualify for the Progressive. (Also, as I recall)
There are countless other examples of games that start at $0.50, or more, I'm not listing them all.
Again, I don't know if you tend to prefer new machines over old, but if you do, those machines probably have a higher minimum bet than they did just a few years ago. The result of that, of course, is that you pop in a twenty and are essentially starting out with fewer spins, so sometimes the $20 goes away faster than it used to.
Vultures can't be choosers.