By comparison with the Retina display of the 4, that's no longer true, but the original iPad was pretty good to start with, at 132 pixels per square inch. Typical computer monitors only have 72. But the Retina iPad 4 display gets 264 pixels into a square inch - both displays are 250mm diagonally, or 9.7 inches in Ye Olde Speech. Definitely, things look super crisp on the 4, and reading is a pleasure. Images, apps and most websites look fantastic.
Four does seem to be the magic number - the 4 also has four times more RAM (1024MB DDR2 RAM compared to 256MB in the 1).
Also, both iPads have an accelerometer, ambient light sensor and magnetometer, but the 4 also has a gyroscope.
Also, considering the 4's sveltitude (OK, I'm sure I didn't make that word up, as much as I would like to flatter myself), it has a much more powerful processor too. The 4 has a 1.4GHz dual-core Apple Swift CPU while the 1 has just one core: an ARM Cortex A8 running at 1GHz.
But the real point is that the millions of pixels it has to light up get a much more powerful graphics processor in the 4: the Quad-core PowerVR SGX554MP4 compared to the 1's PowerVR SGX535.
The wireless protocol might be the same, but Bluetooth in the 4 is advanced over the 1's Bluetooth 2.1+EDR; it has Bluetooth 4 (there's that number again).
The Herald App is a good test, as it can seem to take an age to load on the 1 and we use it every day. It's not as good as the Herald in print when it comes to lighting fires, but it's updated much more often than daily, it's in colour, sometimes it has video clips and hey, there's no newsprint left on your hands.
On the 1 it booted in 14.6 seconds to the point where all the pictures and stories on the Featured page loaded in full. Not actually too bad, I was pleasantly surprised, but it shows how the brain retunes expectations to define 'slow', I guess. In the same room and on the same wireless network (both support 802.11/n wifi), the 4 did the same trick in 1.9 seconds. That's more than seven-and-a-half times faster, despite driving a lot more pixels.
The 4 also gets a much better camera - well, that wouldn't be that hard, since the 1 doesn't have a camera. But the 2 had a .7MP, 720p camera while the 4 has a way better 5MP, 1080p.
Also, despite the differences and potential greater power drain, battery life is (officially, anyway) the same at 10 hours (Wi-Fi), 9 hours (3G/LTE) browsing; 10 hours video; 140 hours audio; 1 month on standby.
So, does this all mean Apple is about to release a new iPad? I would have thought a new iPhone (an inter-generational '5S' or something) was more likely, but we got four generations of iPads in 31 months, not counting the iPad mini. So one every 7.75 months does actually come up to about June. So ... maybe.
Here are some more numbers for you to ponder, though; by the fourth quarter of the year the iPad was introduced, 4.19 million people were using iPads. By the second quarter of 2013, Apple's figures put iPad use at 19.5 million. That's over four times as many users, but of course includes the installed base of pre-4 iPads plus the mini.
If a new one comes out, I might be tempted to buy one as they're fantastic presentation tools. Apart from being able to pass it around, being able to hook it up to a projector is fantastic - the iPad one only supported projecting from Keynote while the newer one's let you show everything you are doing, which is how I prefer to work.
Personally, I don't think iPad has hit its straps as a device yet. A bit more power, then yes, it's getting there. For example, using GarageBand as a kind of musician's audio sketchpad is cool, but limited - more power still and an updated app could potentially make this much more useful, and extrapolate this up through many kinds of apps and the future is bright.