My microwave had an inverter rather than a transformer, which is a change I guess. Don't know if it's an improvement. I do know it was a disappointment to me when the microwave failed after 4 years and I went to salvage the transformer and there wasn't one.
I'd say that is not completely true. Variable power levels (on-off-on-off which certain cheaper microwave ovens do) are definitely not a gimmick, unless you like some parts of your meals cold and other piping hot.